[PATCH v6 0/7] TDX host: kexec/kdump support

[PATCH v6 0/7] TDX host: kexec/kdump support

[Kai Huang]

This series is the latest attempt to support kexec on TDX host following
Dave's suggestion to use a percpu boolean to control WBINVD during
kexec.

Hi Boris/Tom,

Thanks for your review on the first two patches.  Please let me know if
you have more comments.

Hi Dave,

Tom has provided Reviewed-by for the first two patches which change SME
code.  TDX patches also received RBs from multiple Intel TDX developers
(the last patch has Paolo's Acked-by too).  Could you help to review this
series, and if looks good to you, consider merging this series?

v5 -> v6:
 - Regenerate based on latest tip/master.
 - Rename do_seamcall() to __seamcall_dirty_cache() - Rick.
 - Collect Reviewed-by tags from Tom, Rick, Chao (thanks!).

v5: https://lore.kernel.org/kvm/cover.1753679792.git.kai.huang@intel.com/

v4 -> v5:
 - Address comments from Tom, Hpa and Chao (nothing major)
   - RELOC_KERNEL_HOST_MEM_ACTIVE -> RELOC_KERNEL_HOST_MEM_ENC_ACTIVE
     in patch 1 (Tom)
   - Add a comment to explain only RELOC_KERNEL_PRESERVE_CONTEXT is
     restored after jumping back from peer kernel for preserved_context
     kexec in patch 1.
   - Use testb instead of testq to save 3 bytes in patch 1 (Hpa)
   - Remove the unneeded 'ret' local variable in do_seamcall() (Chao)

v4: https://lore.kernel.org/kvm/cover.1752730040.git.kai.huang@intel.com/

v3 -> v4:
 - Rebase to latest tip/master.
 - Add a cleanup patch to consolidate relocate_kernel()'s last two
   function parameters -- Boris.
 - Address comments received -- please see individual patches.
 - Collect tags (Tom, Rick, binbin).

 v3: https://lore.kernel.org/kvm/cover.1750934177.git.kai.huang@intel.com/

(For more history please see v3 coverletter.)

=== More information ===

TDX private memory is memory that is encrypted with private Host Key IDs
(HKID).  If the kernel has ever enabled TDX, part of system memory
remains TDX private memory when kexec happens.  E.g., the PAMT (Physical
Address Metadata Table) pages used by the TDX module to track each TDX
memory page's state are never freed once the TDX module is initialized.
TDX guests also have guest private memory and secure-EPT pages.

After kexec, the new kernel will have no knowledge of which memory page
was used as TDX private page and can use all memory as regular memory.

1) Cache flush

Per TDX 1.5 base spec "8.6.1.Platforms not Using ACT: Required Cache
Flush and Initialization by the Host VMM", to support kexec for TDX, the
kernel needs to flush cache to make sure there's no dirty cachelines of
TDX private memory left over to the new kernel (when the TDX module
reports TDX_FEATURES.CLFLUSH_BEFORE_ALLOC as 1 in the global metadata for
the platform).  The kernel also needs to make sure there's no more TDX
activity (no SEAMCALL) after cache flush so that no new dirty cachelines
of TDX private memory are generated.

SME has similar requirement.  SME kexec support uses WBINVD to do the
cache flush.  WBINVD is able to flush cachelines associated with any
HKID.  Reuse the WBINVD introduced by SME to flush cache for TDX.

Currently the kernel explicitly checks whether the hardware supports SME
and only does WBINVD if true.  Instead of adding yet another TDX
specific check, this series uses a percpu boolean to indicate whether
WBINVD is needed on that CPU during kexec.

2) Reset TDX private memory using MOVDIR64B

The TDX spec (the aforementioned section) also suggests the kernel
*should* use MOVDIR64B to clear TDX private page before the kernel
reuses it as regular one.

However, in reality the situation can be more flexible.  Per TDX 1.5
base spec ("Table 16.2: Non-ACT Platforms Checks on Memory Reads in Ci
Mode" and "Table 16.3: Non-ACT Platforms Checks on Memory Reads in Li
Mode"), the read/write to TDX private memory using shared KeyID without
integrity check enabled will not poison the memory and cause machine
check.

Note on the platforms with ACT (Access Control Table), there's no
integrity check involved thus no machine check is possible to happen due
to memory read/write using different KeyIDs.

KeyID 0 (TME key) doesn't support integrity check.  This series chooses
to NOT reset TDX private memory but leave TDX private memory as-is to the
new kernel.  As mentioned above, in practice it is safe to do so.

3) One limitation

If the kernel has ever enabled TDX, after kexec the new kernel won't be
able to use TDX anymore.  This is because when the new kernel tries to
initialize TDX module it will fail on the first SEAMCALL due to the
module has already been initialized by the old kernel.

More (non-trivial) work will be needed for the new kernel to use TDX,
e.g., one solution is to just reload the TDX module from the location
where BIOS loads the TDX module (/boot/efi/EFI/TDX/).  This series
doesn't cover this, but leave this as future work.

4) Kdump support

This series also enables kdump with TDX, but no special handling is
needed for crash kexec (except turning on the Kconfig option):

 - kdump kernel uses reserved memory from the old kernel as system ram,
   and the old kernel will never use the reserved memory as TDX memory.
 - /proc/vmcore contains TDX private memory pages.  It's meaningless to
   read them, but it doesn't do any harm either.

5) TDX "partial write machine check" erratum

On the platform with TDX erratum, a partial write (a write transaction
of less than a cacheline lands at memory controller) to TDX private
memory poisons that memory, and a subsequent read triggers machine
check.  On those platforms, the kernel needs to reset TDX private memory
before jumping to the new kernel otherwise the new kernel may see
unexpected machine check.

The kernel currently doesn't track which page is TDX private memory.
It's not trivial to reset TDX private memory.  For simplicity, this
series simply disables kexec/kdump for such platforms.  This can be
enhanced in the future.


Kai Huang (7):
  x86/kexec: Consolidate relocate_kernel() function parameters
  x86/sme: Use percpu boolean to control WBINVD during kexec
  x86/virt/tdx: Mark memory cache state incoherent when making SEAMCALL
  x86/kexec: Disable kexec/kdump on platforms with TDX partial write
    erratum
  x86/virt/tdx: Remove the !KEXEC_CORE dependency
  x86/virt/tdx: Update the kexec section in the TDX documentation
  KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

 Documentation/arch/x86/tdx.rst       | 14 ++++-----
 arch/x86/Kconfig                     |  1 -
 arch/x86/include/asm/kexec.h         | 12 ++++++--
 arch/x86/include/asm/processor.h     |  2 ++
 arch/x86/include/asm/tdx.h           | 27 ++++++++++++++++-
 arch/x86/kernel/cpu/amd.c            | 17 +++++++++++
 arch/x86/kernel/machine_kexec_64.c   | 44 ++++++++++++++++++++++------
 arch/x86/kernel/process.c            | 24 +++++++--------
 arch/x86/kernel/relocate_kernel_64.S | 36 +++++++++++++++--------
 arch/x86/kvm/vmx/tdx.c               | 12 ++++++++
 arch/x86/virt/vmx/tdx/tdx.c          | 16 ++++++++--
 11 files changed, 158 insertions(+), 47 deletions(-)


base-commit: 4b6b14d20bc04dcab6dd3ad0d5a50a0f473d1c18
-- 
2.50.1

[PATCH v6 1/7] x86/kexec: Consolidate relocate_kernel() function parameters

[Kai Huang]

During kexec, the kernel jumps to the new kernel in relocate_kernel(),
which is implemented in assembly and both 32-bit and 64-bit have their
own version.

Currently, for both 32-bit and 64-bit, the last two parameters of the
relocate_kernel() are both 'unsigned int' but actually they only convey
a boolean, i.e., one bit information.  The 'unsigned int' has enough
space to carry two bits information therefore there's no need to pass
the two booleans in two separate 'unsigned int'.

Consolidate the last two function parameters of relocate_kernel() into a
single 'unsigned int' and pass flags instead.

Only consolidate the 64-bit version albeit the similar optimization can
be done for the 32-bit version too.  Don't bother changing the 32-bit
version while it is working (since assembly code change is required).

Signed-off-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
---

 v5 -> v6:
  - Add Tom's RB.

 v4 -> v5:
  - RELOC_KERNEL_HOST_MEM_ACTIVE -> RELOC_KERNEL_HOST_MEM_ENC_ACTIVE
    (Tom)
  - Add a comment to explain only RELOC_KERNEL_PRESERVE_CONTEXT is
    restored after jumping back from peer kernel for preserved_context
    kexec (pointed out by Tom).
  - Use testb instead of testq when comparing the flag with R11 to save
    3 bytes (Hpa).

 v4:
  - new patch


---
 arch/x86/include/asm/kexec.h         | 12 ++++++++++--
 arch/x86/kernel/machine_kexec_64.c   | 22 +++++++++++++---------
 arch/x86/kernel/relocate_kernel_64.S | 25 +++++++++++++++----------
 3 files changed, 38 insertions(+), 21 deletions(-)

diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
index f2ad77929d6e..12cebbcdb6c8 100644
--- a/arch/x86/include/asm/kexec.h
+++ b/arch/x86/include/asm/kexec.h
@@ -13,6 +13,15 @@
 # define KEXEC_DEBUG_EXC_HANDLER_SIZE	6 /* PUSHI, PUSHI, 2-byte JMP */
 #endif
 
+#ifdef CONFIG_X86_64
+
+#include <linux/bits.h>
+
+#define RELOC_KERNEL_PRESERVE_CONTEXT		BIT(0)
+#define RELOC_KERNEL_HOST_MEM_ENC_ACTIVE	BIT(1)
+
+#endif
+
 # define KEXEC_CONTROL_PAGE_SIZE	4096
 # define KEXEC_CONTROL_CODE_MAX_SIZE	2048
 
@@ -121,8 +130,7 @@ typedef unsigned long
 relocate_kernel_fn(unsigned long indirection_page,
 		   unsigned long pa_control_page,
 		   unsigned long start_address,
-		   unsigned int preserve_context,
-		   unsigned int host_mem_enc_active);
+		   unsigned int flags);
 #endif
 extern relocate_kernel_fn relocate_kernel;
 #define ARCH_HAS_KIMAGE_ARCH
diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index 697fb99406e6..5cda8d8d8b13 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -384,16 +384,10 @@ void __nocfi machine_kexec(struct kimage *image)
 {
 	unsigned long reloc_start = (unsigned long)__relocate_kernel_start;
 	relocate_kernel_fn *relocate_kernel_ptr;
-	unsigned int host_mem_enc_active;
+	unsigned int relocate_kernel_flags;
 	int save_ftrace_enabled;
 	void *control_page;
 
-	/*
-	 * This must be done before load_segments() since if call depth tracking
-	 * is used then GS must be valid to make any function calls.
-	 */
-	host_mem_enc_active = cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT);
-
 #ifdef CONFIG_KEXEC_JUMP
 	if (image->preserve_context)
 		save_processor_state();
@@ -427,6 +421,17 @@ void __nocfi machine_kexec(struct kimage *image)
 	 */
 	relocate_kernel_ptr = control_page + (unsigned long)relocate_kernel - reloc_start;
 
+	relocate_kernel_flags = 0;
+	if (image->preserve_context)
+		relocate_kernel_flags |= RELOC_KERNEL_PRESERVE_CONTEXT;
+
+	/*
+	 * This must be done before load_segments() since if call depth tracking
+	 * is used then GS must be valid to make any function calls.
+	 */
+	if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT))
+		relocate_kernel_flags |= RELOC_KERNEL_HOST_MEM_ENC_ACTIVE;
+
 	/*
 	 * The segment registers are funny things, they have both a
 	 * visible and an invisible part.  Whenever the visible part is
@@ -443,8 +448,7 @@ void __nocfi machine_kexec(struct kimage *image)
 	image->start = relocate_kernel_ptr((unsigned long)image->head,
 					   virt_to_phys(control_page),
 					   image->start,
-					   image->preserve_context,
-					   host_mem_enc_active);
+					   relocate_kernel_flags);
 
 #ifdef CONFIG_KEXEC_JUMP
 	if (image->preserve_context)
diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index ea604f4d0b52..26e945f85d19 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -66,8 +66,7 @@ SYM_CODE_START_NOALIGN(relocate_kernel)
 	 * %rdi indirection_page
 	 * %rsi pa_control_page
 	 * %rdx start address
-	 * %rcx preserve_context
-	 * %r8  host_mem_enc_active
+	 * %rcx flags: RELOC_KERNEL_*
 	 */
 
 	/* Save the CPU context, used for jumping back */
@@ -111,7 +110,7 @@ SYM_CODE_START_NOALIGN(relocate_kernel)
 	/* save indirection list for jumping back */
 	movq	%rdi, pa_backup_pages_map(%rip)
 
-	/* Save the preserve_context to %r11 as swap_pages clobbers %rcx. */
+	/* Save the flags to %r11 as swap_pages clobbers %rcx. */
 	movq	%rcx, %r11
 
 	/* setup a new stack at the end of the physical control page */
@@ -129,9 +128,8 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 	/*
 	 * %rdi	indirection page
 	 * %rdx start address
-	 * %r8 host_mem_enc_active
 	 * %r9 page table page
-	 * %r11 preserve_context
+	 * %r11 flags: RELOC_KERNEL_*
 	 * %r13 original CR4 when relocate_kernel() was invoked
 	 */
 
@@ -204,7 +202,7 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 	 * entries that will conflict with the now unencrypted memory
 	 * used by kexec. Flush the caches before copying the kernel.
 	 */
-	testq	%r8, %r8
+	testb	$RELOC_KERNEL_HOST_MEM_ENC_ACTIVE, %r11b
 	jz .Lsme_off
 	wbinvd
 .Lsme_off:
@@ -220,7 +218,7 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 	movq	%cr3, %rax
 	movq	%rax, %cr3
 
-	testq	%r11, %r11	/* preserve_context */
+	testb	$RELOC_KERNEL_PRESERVE_CONTEXT, %r11b
 	jnz .Lrelocate
 
 	/*
@@ -273,7 +271,13 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 	ANNOTATE_NOENDBR
 	andq	$PAGE_MASK, %r8
 	lea	PAGE_SIZE(%r8), %rsp
-	movl	$1, %r11d	/* Ensure preserve_context flag is set */
+	/*
+	 * Ensure RELOC_KERNEL_PRESERVE_CONTEXT flag is set so that
+	 * swap_pages() can swap pages correctly.  Note all other
+	 * RELOC_KERNEL_* flags passed to relocate_kernel() are not
+	 * restored.
+	 */
+	movl	$RELOC_KERNEL_PRESERVE_CONTEXT, %r11d
 	call	swap_pages
 	movq	kexec_va_control_page(%rip), %rax
 0:	addq	$virtual_mapped - 0b, %rax
@@ -321,7 +325,7 @@ SYM_CODE_START_LOCAL_NOALIGN(swap_pages)
 	UNWIND_HINT_END_OF_STACK
 	/*
 	 * %rdi indirection page
-	 * %r11 preserve_context
+	 * %r11 flags: RELOC_KERNEL_*
 	 */
 	movq	%rdi, %rcx	/* Put the indirection_page in %rcx */
 	xorl	%edi, %edi
@@ -357,7 +361,8 @@ SYM_CODE_START_LOCAL_NOALIGN(swap_pages)
 	movq	%rdi, %rdx    /* Save destination page to %rdx */
 	movq	%rsi, %rax    /* Save source page to %rax */
 
-	testq	%r11, %r11    /* Only actually swap for ::preserve_context */
+	/* Only actually swap for ::preserve_context */
+	testb	$RELOC_KERNEL_PRESERVE_CONTEXT, %r11b
 	jz	.Lnoswap
 
 	/* copy source page to swap page */
-- 
2.50.1

[PATCH v6 2/7] x86/sme: Use percpu boolean to control WBINVD during kexec

[Kai Huang]

TL;DR:

Prepare to unify how TDX and SME do cache flushing during kexec by
making a percpu boolean control whether to do the WBINVD.

-- Background --

On SME platforms, dirty cacheline aliases with and without encryption
bit can coexist, and the CPU can flush them back to memory in random
order.  During kexec, the caches must be flushed before jumping to the
new kernel otherwise the dirty cachelines could silently corrupt the
memory used by the new kernel due to different encryption property.

TDX also needs a cache flush during kexec for the same reason.  It would
be good to have a generic way to flush the cache instead of scattering
checks for each feature all around.

When SME is enabled, the kernel basically encrypts all memory including
the kernel itself and a simple memory write from the kernel could dirty
cachelines.  Currently, the kernel uses WBINVD to flush the cache for
SME during kexec in two places:

1) the one in stop_this_cpu() for all remote CPUs when the kexec-ing CPU
   stops them;
2) the one in the relocate_kernel() where the kexec-ing CPU jumps to the
   new kernel.

-- Solution --

Unlike SME, TDX can only dirty cachelines when it is used (i.e., when
SEAMCALLs are performed).  Since there are no more SEAMCALLs after the
aforementioned WBINVDs, leverage this for TDX.

To unify the approach for SME and TDX, use a percpu boolean to indicate
the cache may be in an incoherent state and needs flushing during kexec,
and set the boolean for SME.  TDX can then leverage it.

While SME could use a global flag (since it's enabled at early boot and
enabled on all CPUs), the percpu flag fits TDX better:

The percpu flag can be set when a CPU makes a SEAMCALL, and cleared when
another WBINVD on the CPU obviates the need for a kexec-time WBINVD.
Saving kexec-time WBINVD is valuable, because there is an existing
race[*] where kexec could proceed while another CPU is active.  WBINVD
could make this race worse, so it's worth skipping it when possible.

-- Side effect to SME --

Today the first WBINVD in the stop_this_cpu() is performed when SME is
*supported* by the platform, and the second WBINVD is done in
relocate_kernel() when SME is *activated* by the kernel.  Make things
simple by changing to do the second WBINVD when the platform supports
SME.  This allows the kernel to simply turn on this percpu boolean when
bringing up a CPU by checking whether the platform supports SME.

No other functional change intended.

[*] The aforementioned race:

During kexec native_stop_other_cpus() is called to stop all remote CPUs
before jumping to the new kernel.  native_stop_other_cpus() firstly
sends normal REBOOT vector IPIs to stop remote CPUs and waits them to
stop.  If that times out, it sends NMI to stop the CPUs that are still
alive.  The race happens when native_stop_other_cpus() has to send NMIs
and could potentially result in the system hang (for more information
please see [1]).

Link: https://lore.kernel.org/kvm/b963fcd60abe26c7ec5dc20b42f1a2ebbcc72397.1750934177.git.kai.huang@intel.com/ [1]
Signed-off-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Tested-by: Tom Lendacky <thomas.lendacky@amd.com>
---

v5 -> v6:
 - No change

v4 -> v5:
 - Code rebase due to change RELOC_KERNEL_HOST_MEM_ACTIVE to
   RELOC_KERNEL_HOST_MEM_ENC_ACTIVE.

v3 -> v4:
 - Simplify the changelog using AI -- Boris
 - Call out "Test CPUID bit directly due to mem_encrypt=off" in the
   comment  -- Boris
 - Add a comment to explain the percpu boolean -- Boris
 - s/wbinvd/WBINVD -- Boris
 - Code update due to patch 1 being added


---
 arch/x86/include/asm/kexec.h         |  4 ++--
 arch/x86/include/asm/processor.h     |  2 ++
 arch/x86/kernel/cpu/amd.c            | 17 +++++++++++++++++
 arch/x86/kernel/machine_kexec_64.c   | 14 ++++++++++----
 arch/x86/kernel/process.c            | 24 +++++++++++-------------
 arch/x86/kernel/relocate_kernel_64.S | 13 ++++++++++---
 6 files changed, 52 insertions(+), 22 deletions(-)

diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
index 12cebbcdb6c8..5cfb27f26583 100644
--- a/arch/x86/include/asm/kexec.h
+++ b/arch/x86/include/asm/kexec.h
@@ -17,8 +17,8 @@
 
 #include <linux/bits.h>
 
-#define RELOC_KERNEL_PRESERVE_CONTEXT		BIT(0)
-#define RELOC_KERNEL_HOST_MEM_ENC_ACTIVE	BIT(1)
+#define RELOC_KERNEL_PRESERVE_CONTEXT	BIT(0)
+#define RELOC_KERNEL_CACHE_INCOHERENT	BIT(1)
 
 #endif
 
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index bde58f6510ac..a24c7805acdb 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -731,6 +731,8 @@ void __noreturn stop_this_cpu(void *dummy);
 void microcode_check(struct cpuinfo_x86 *prev_info);
 void store_cpu_caps(struct cpuinfo_x86 *info);
 
+DECLARE_PER_CPU(bool, cache_state_incoherent);
+
 enum l1tf_mitigations {
 	L1TF_MITIGATION_OFF,
 	L1TF_MITIGATION_AUTO,
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index a5ece6ebe8a7..66a682be4a1a 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -545,6 +545,23 @@ static void early_detect_mem_encrypt(struct cpuinfo_x86 *c)
 {
 	u64 msr;
 
+	/*
+	 * Mark using WBINVD is needed during kexec on processors that
+	 * support SME. This provides support for performing a successful
+	 * kexec when going from SME inactive to SME active (or vice-versa).
+	 *
+	 * The cache must be cleared so that if there are entries with the
+	 * same physical address, both with and without the encryption bit,
+	 * they don't race each other when flushed and potentially end up
+	 * with the wrong entry being committed to memory.
+	 *
+	 * Test the CPUID bit directly because with mem_encrypt=off the
+	 * BSP will clear the X86_FEATURE_SME bit and the APs will not
+	 * see it set after that.
+	 */
+	if (c->extended_cpuid_level >= 0x8000001f && (cpuid_eax(0x8000001f) & BIT(0)))
+		__this_cpu_write(cache_state_incoherent, true);
+
 	/*
 	 * BIOS support is required for SME and SEV.
 	 *   For SME: If BIOS has enabled SME then adjust x86_phys_bits by
diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index 5cda8d8d8b13..dfb91091f451 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -29,6 +29,7 @@
 #include <asm/set_memory.h>
 #include <asm/cpu.h>
 #include <asm/efi.h>
+#include <asm/processor.h>
 
 #ifdef CONFIG_ACPI
 /*
@@ -426,11 +427,11 @@ void __nocfi machine_kexec(struct kimage *image)
 		relocate_kernel_flags |= RELOC_KERNEL_PRESERVE_CONTEXT;
 
 	/*
-	 * This must be done before load_segments() since if call depth tracking
-	 * is used then GS must be valid to make any function calls.
+	 * This must be done before load_segments() since it resets
+	 * GS to 0 and percpu data needs the correct GS to work.
 	 */
-	if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT))
-		relocate_kernel_flags |= RELOC_KERNEL_HOST_MEM_ENC_ACTIVE;
+	if (this_cpu_read(cache_state_incoherent))
+		relocate_kernel_flags |= RELOC_KERNEL_CACHE_INCOHERENT;
 
 	/*
 	 * The segment registers are funny things, they have both a
@@ -441,6 +442,11 @@ void __nocfi machine_kexec(struct kimage *image)
 	 *
 	 * Take advantage of this here by force loading the segments,
 	 * before the GDT is zapped with an invalid value.
+	 *
+	 * load_segments() resets GS to 0.  Don't make any function call
+	 * after here since call depth tracking uses percpu variables to
+	 * operate (relocate_kernel() is explicitly ignored by call depth
+	 * tracking).
 	 */
 	load_segments();
 
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 1b7960cf6eb0..f2bbbeef5477 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -88,6 +88,16 @@ EXPORT_PER_CPU_SYMBOL(cpu_tss_rw);
 DEFINE_PER_CPU(bool, __tss_limit_invalid);
 EXPORT_PER_CPU_SYMBOL_GPL(__tss_limit_invalid);
 
+/*
+ * The cache may be in an incoherent state and needs flushing during kexec.
+ * E.g., on SME/TDX platforms, dirty cacheline aliases with and without
+ * encryption bit(s) can coexist and the cache needs to be flushed before
+ * booting to the new kernel to avoid the silent memory corruption due to
+ * dirty cachelines with different encryption property being written back
+ * to the memory.
+ */
+DEFINE_PER_CPU(bool, cache_state_incoherent);
+
 /*
  * this gets called so that we can store lazy state into memory and copy the
  * current task into the new thread.
@@ -827,19 +837,7 @@ void __noreturn stop_this_cpu(void *dummy)
 	disable_local_APIC();
 	mcheck_cpu_clear(c);
 
-	/*
-	 * Use wbinvd on processors that support SME. This provides support
-	 * for performing a successful kexec when going from SME inactive
-	 * to SME active (or vice-versa). The cache must be cleared so that
-	 * if there are entries with the same physical address, both with and
-	 * without the encryption bit, they don't race each other when flushed
-	 * and potentially end up with the wrong entry being committed to
-	 * memory.
-	 *
-	 * Test the CPUID bit directly because the machine might've cleared
-	 * X86_FEATURE_SME due to cmdline options.
-	 */
-	if (c->extended_cpuid_level >= 0x8000001f && (cpuid_eax(0x8000001f) & BIT(0)))
+	if (this_cpu_read(cache_state_incoherent))
 		wbinvd();
 
 	/*
diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 26e945f85d19..11e20bb13aca 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -198,14 +198,21 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 	movq	%r9, %cr3
 
 	/*
+	 * If the memory cache is in incoherent state, e.g., due to
+	 * memory encryption, do WBINVD to flush cache.
+	 *
 	 * If SME is active, there could be old encrypted cache line
 	 * entries that will conflict with the now unencrypted memory
 	 * used by kexec. Flush the caches before copying the kernel.
+	 *
+	 * Note SME sets this flag to true when the platform supports
+	 * SME, so the WBINVD is performed even SME is not activated
+	 * by the kernel.  But this has no harm.
 	 */
-	testb	$RELOC_KERNEL_HOST_MEM_ENC_ACTIVE, %r11b
-	jz .Lsme_off
+	testb	$RELOC_KERNEL_CACHE_INCOHERENT, %r11b
+	jz .Lnowbinvd
 	wbinvd
-.Lsme_off:
+.Lnowbinvd:
 
 	call	swap_pages
 
-- 
2.50.1

[PATCH v6 3/7] x86/virt/tdx: Mark memory cache state incoherent when making SEAMCALL

[Kai Huang]

On TDX platforms, dirty cacheline aliases with and without encryption
bits can coexist, and the cpu can flush them back to memory in random
order.  During kexec, the caches must be flushed before jumping to the
new kernel otherwise the dirty cachelines could silently corrupt the
memory used by the new kernel due to different encryption property.

A percpu boolean is used to mark whether the cache of a given CPU may be
in an incoherent state, and the kexec performs WBINVD on the CPUs with
that boolean turned on.

For TDX, only the TDX module or the TDX guests can generate dirty
cachelines of TDX private memory, i.e., they are only generated when the
kernel does a SEAMCALL.

Set that boolean when the kernel does SEAMCALL so that kexec can flush
the cache correctly.

The kernel provides both the __seamcall*() assembly functions and the
seamcall*() wrapper ones which additionally handle running out of
entropy error in a loop.  Most of the SEAMCALLs are called using the
seamcall*(), except TDH.VP.ENTER and TDH.PHYMEM.PAGE.RDMD which are
called using __seamcall*() variant directly.

To cover the two special cases, add a new __seamcall_dirty_cache()
helper which only sets the percpu boolean and calls the __seamcall*(),
and change the special cases to use the new helper.  To cover all other
SEAMCALLs, change seamcall*() to call the new helper.

For the SEAMCALLs invoked via seamcall*(), they can be made from both
task context and IRQ disabled context.  Given SEAMCALL is just a lengthy
instruction (e.g., thousands of cycles) from kernel's point of view and
preempt_{disable|enable}() is cheap compared to it, just unconditionally
disable preemption during setting the boolean and making SEAMCALL.

Signed-off-by: Kai Huang <kai.huang@intel.com>
Tested-by: Farrah Chen <farrah.chen@intel.com>
Reviewed-by: Chao Gao <chao.gao@intel.com>
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---

v5 -> v6:
 - Rename do_seamcall() to __seamcall_dirty_cache() - Rick.
 - Add Rick and Chao's RB.

v4 -> v5:
 - Remove unneeded 'ret' local variable in do_seamcall() - Chao.

v3 -> v4:
 - Set the boolean for TDH.VP.ENTER and TDH.PHYMEM.PAGE.RDMD. -Rick
 - Update the first paragraph to make it shorter -- Rick
 - Update changelog to mention the two special cases.


---
 arch/x86/include/asm/tdx.h  | 25 ++++++++++++++++++++++++-
 arch/x86/virt/vmx/tdx/tdx.c |  4 ++--
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index 7ddef3a69866..0922265c6bdc 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -102,10 +102,31 @@ u64 __seamcall_ret(u64 fn, struct tdx_module_args *args);
 u64 __seamcall_saved_ret(u64 fn, struct tdx_module_args *args);
 void tdx_init(void);
 
+#include <linux/preempt.h>
 #include <asm/archrandom.h>
+#include <asm/processor.h>
 
 typedef u64 (*sc_func_t)(u64 fn, struct tdx_module_args *args);
 
+static __always_inline u64 __seamcall_dirty_cache(sc_func_t func, u64 fn,
+						  struct tdx_module_args *args)
+{
+	lockdep_assert_preemption_disabled();
+
+	/*
+	 * SEAMCALLs are made to the TDX module and can generate dirty
+	 * cachelines of TDX private memory.  Mark cache state incoherent
+	 * so that the cache can be flushed during kexec.
+	 *
+	 * This needs to be done before actually making the SEAMCALL,
+	 * because kexec-ing CPU could send NMI to stop remote CPUs,
+	 * in which case even disabling IRQ won't help here.
+	 */
+	this_cpu_write(cache_state_incoherent, true);
+
+	return func(fn, args);
+}
+
 static __always_inline u64 sc_retry(sc_func_t func, u64 fn,
 			   struct tdx_module_args *args)
 {
@@ -113,7 +134,9 @@ static __always_inline u64 sc_retry(sc_func_t func, u64 fn,
 	u64 ret;
 
 	do {
-		ret = func(fn, args);
+		preempt_disable();
+		ret = __seamcall_dirty_cache(func, fn, args);
+		preempt_enable();
 	} while (ret == TDX_RND_NO_ENTROPY && --retry);
 
 	return ret;
diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index c7a9a087ccaf..3ea6f587c81a 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -1266,7 +1266,7 @@ static bool paddr_is_tdx_private(unsigned long phys)
 		return false;
 
 	/* Get page type from the TDX module */
-	sret = __seamcall_ret(TDH_PHYMEM_PAGE_RDMD, &args);
+	sret = __seamcall_dirty_cache(__seamcall_ret, TDH_PHYMEM_PAGE_RDMD, &args);
 
 	/*
 	 * The SEAMCALL will not return success unless there is a
@@ -1522,7 +1522,7 @@ noinstr __flatten u64 tdh_vp_enter(struct tdx_vp *td, struct tdx_module_args *ar
 {
 	args->rcx = tdx_tdvpr_pa(td);
 
-	return __seamcall_saved_ret(TDH_VP_ENTER, args);
+	return __seamcall_dirty_cache(__seamcall_saved_ret, TDH_VP_ENTER, args);
 }
 EXPORT_SYMBOL_GPL(tdh_vp_enter);
 
-- 
2.50.1

[PATCH v6 4/7] x86/kexec: Disable kexec/kdump on platforms with TDX partial write erratum

[Kai Huang]

Some early TDX-capable platforms have an erratum: A kernel partial
write (a write transaction of less than cacheline lands at memory
controller) to TDX private memory poisons that memory, and a subsequent
read triggers a machine check.

On those platforms, the old kernel must reset TDX private memory before
jumping to the new kernel, otherwise the new kernel may see unexpected
machine check.  Currently the kernel doesn't track which page is a TDX
private page.  For simplicity just fail kexec/kdump for those platforms.

Leverage the existing machine_kexec_prepare() to fail kexec/kdump by
adding the check of the presence of the TDX erratum (which is only
checked for if the kernel is built with TDX host support).  This rejects
kexec/kdump when the kernel is loading the kexec/kdump kernel image.

The alternative is to reject kexec/kdump when the kernel is jumping to
the new kernel.  But for kexec this requires adding a new check (e.g.,
arch_kexec_allowed()) in the common code to fail kernel_kexec() at early
stage.  Kdump (crash_kexec()) needs similar check, but it's hard to
justify because crash_kexec() is not supposed to abort.

It's feasible to further relax this limitation, i.e., only fail kexec
when TDX is actually enabled by the kernel.  But this is still a half
measure compared to resetting TDX private memory so just do the simplest
thing for now.

The impact to userspace is the users will get an error when loading the
kexec/kdump kernel image:

  kexec_load failed: Operation not supported

This might be confusing to the users, thus also print the reason in the
dmesg:

  [..] kexec: Not allowed on platform with tdx_pw_mce bug.

Signed-off-by: Kai Huang <kai.huang@intel.com>
Tested-by: Farrah Chen <farrah.chen@intel.com>
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
 arch/x86/kernel/machine_kexec_64.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index dfb91091f451..15088d14904f 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -347,6 +347,22 @@ int machine_kexec_prepare(struct kimage *image)
 	unsigned long reloc_end = (unsigned long)__relocate_kernel_end;
 	int result;
 
+	/*
+	 * Some early TDX-capable platforms have an erratum.  A kernel
+	 * partial write (a write transaction of less than cacheline
+	 * lands at memory controller) to TDX private memory poisons that
+	 * memory, and a subsequent read triggers a machine check.
+	 *
+	 * On those platforms the old kernel must reset TDX private
+	 * memory before jumping to the new kernel otherwise the new
+	 * kernel may see unexpected machine check.  For simplicity
+	 * just fail kexec/kdump on those platforms.
+	 */
+	if (boot_cpu_has_bug(X86_BUG_TDX_PW_MCE)) {
+		pr_info_once("Not allowed on platform with tdx_pw_mce bug\n");
+		return -EOPNOTSUPP;
+	}
+
 	/* Setup the identity mapped 64bit page table */
 	result = init_pgtable(image, __pa(control_page));
 	if (result)
-- 
2.50.1

[PATCH v6 5/7] x86/virt/tdx: Remove the !KEXEC_CORE dependency

[Kai Huang]

During kexec it is now guaranteed that all dirty cachelines of TDX
private memory are flushed before jumping to the new kernel.  The TDX
private memory from the old kernel will remain as TDX private memory in
the new kernel, but it is OK because kernel read/write to TDX private
memory will never cause machine check, except on the platforms with the
TDX partial write erratum, which has already been handled.

It is safe to allow kexec to work together with TDX now.  Remove the
!KEXEC_CORE dependency.

Signed-off-by: Kai Huang <kai.huang@intel.com>
Tested-by: Farrah Chen <farrah.chen@intel.com>
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
 arch/x86/Kconfig | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 58d890fe2100..e2cbfb021bc6 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1896,7 +1896,6 @@ config INTEL_TDX_HOST
 	depends on X86_X2APIC
 	select ARCH_KEEP_MEMBLOCK
 	depends on CONTIG_ALLOC
-	depends on !KEXEC_CORE
 	depends on X86_MCE
 	help
 	  Intel Trust Domain Extensions (TDX) protects guest VMs from malicious
-- 
2.50.1

[PATCH v6 6/7] x86/virt/tdx: Update the kexec section in the TDX documentation

[Kai Huang]

TDX host kernel now supports kexec/kdump.  Update the documentation to
reflect that.

Opportunistically, remove the parentheses in "Kexec()" and move this
section under the "Erratum" section because the updated "Kexec" section
now refers to that erratum.

Signed-off-by: Kai Huang <kai.huang@intel.com>
Tested-by: Farrah Chen <farrah.chen@intel.com>
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
 Documentation/arch/x86/tdx.rst | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/Documentation/arch/x86/tdx.rst b/Documentation/arch/x86/tdx.rst
index 719043cd8b46..61670e7df2f7 100644
--- a/Documentation/arch/x86/tdx.rst
+++ b/Documentation/arch/x86/tdx.rst
@@ -142,13 +142,6 @@ but depends on the BIOS to behave correctly.
 Note TDX works with CPU logical online/offline, thus the kernel still
 allows to offline logical CPU and online it again.
 
-Kexec()
-~~~~~~~
-
-TDX host support currently lacks the ability to handle kexec.  For
-simplicity only one of them can be enabled in the Kconfig.  This will be
-fixed in the future.
-
 Erratum
 ~~~~~~~
 
@@ -171,6 +164,13 @@ If the platform has such erratum, the kernel prints additional message in
 machine check handler to tell user the machine check may be caused by
 kernel bug on TDX private memory.
 
+Kexec
+~~~~~~~
+
+Currently kexec doesn't work on the TDX platforms with the aforementioned
+erratum.  It fails when loading the kexec kernel image.  Otherwise it
+works normally.
+
 Interaction vs S3 and deeper states
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-- 
2.50.1

[PATCH v6 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

[Kai Huang]

On TDX platforms, during kexec, the kernel needs to make sure there are
no dirty cachelines of TDX private memory before booting to the new
kernel to avoid silent memory corruption to the new kernel.

During kexec, the kexec-ing CPU firstly invokes native_stop_other_cpus()
to stop all remote CPUs before booting to the new kernel.  The remote
CPUs will then execute stop_this_cpu() to stop themselves.

The kernel has a percpu boolean to indicate whether the cache of a CPU
may be in incoherent state.  In stop_this_cpu(), the kernel does WBINVD
if that percpu boolean is true.

TDX turns on that percpu boolean on a CPU when the kernel does SEAMCALL.
This makes sure the caches will be flushed during kexec.

However, the native_stop_other_cpus() and stop_this_cpu() have a "race"
which is extremely rare to happen but could cause the system to hang.

Specifically, the native_stop_other_cpus() firstly sends normal reboot
IPI to remote CPUs and waits one second for them to stop.  If that times
out, native_stop_other_cpus() then sends NMIs to remote CPUs to stop
them.

The aforementioned race happens when NMIs are sent.  Doing WBINVD in
stop_this_cpu() makes each CPU take longer time to stop and increases
the chance of the race happening.

Explicitly flush cache in tdx_disable_virtualization_cpu() after which
no more TDX activity can happen on this cpu.  This moves the WBINVD to
an earlier stage than stop_this_cpus(), avoiding a possibly lengthy
operation at a time where it could cause this race.

Signed-off-by: Kai Huang <kai.huang@intel.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Tested-by: Farrah Chen <farrah.chen@intel.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: Chao Gao <chao.gao@intel.com>
---

v5 -> v6:
 - Add Chao's RB.

v4 -> v5:
 - No change

v3 -> v4:
 - Change doing wbinvd() from rebooting notifier to
   tdx_disable_virtualization_cpu() to cover the case where more
   SEAMCALL can be made after cache flush, i.e., doing kexec when
   there's TD alive.  - Chao.
 - Add check to skip wbinvd if the boolean is false. -- Chao
 - Fix typo in the comment -- Binbin.


---
 arch/x86/include/asm/tdx.h  |  2 ++
 arch/x86/kvm/vmx/tdx.c      | 12 ++++++++++++
 arch/x86/virt/vmx/tdx/tdx.c | 12 ++++++++++++
 3 files changed, 26 insertions(+)

diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index 0922265c6bdc..e9a213582f03 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -217,6 +217,7 @@ u64 tdh_mem_page_remove(struct tdx_td *td, u64 gpa, u64 level, u64 *ext_err1, u6
 u64 tdh_phymem_cache_wb(bool resume);
 u64 tdh_phymem_page_wbinvd_tdr(struct tdx_td *td);
 u64 tdh_phymem_page_wbinvd_hkid(u64 hkid, struct page *page);
+void tdx_cpu_flush_cache(void);
 #else
 static inline void tdx_init(void) { }
 static inline int tdx_cpu_enable(void) { return -ENODEV; }
@@ -224,6 +225,7 @@ static inline int tdx_enable(void)  { return -ENODEV; }
 static inline u32 tdx_get_nr_guest_keyids(void) { return 0; }
 static inline const char *tdx_dump_mce_info(struct mce *m) { return NULL; }
 static inline const struct tdx_sys_info *tdx_get_sysinfo(void) { return NULL; }
+static inline void tdx_cpu_flush_cache(void) { }
 #endif	/* CONFIG_INTEL_TDX_HOST */
 
 #endif /* !__ASSEMBLER__ */
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 66744f5768c8..1bc6f52e0cd7 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -442,6 +442,18 @@ void tdx_disable_virtualization_cpu(void)
 		tdx_flush_vp(&arg);
 	}
 	local_irq_restore(flags);
+
+	/*
+	 * No more TDX activity on this CPU from here.  Flush cache to
+	 * avoid having to do WBINVD in stop_this_cpu() during kexec.
+	 *
+	 * Kexec calls native_stop_other_cpus() to stop remote CPUs
+	 * before booting to new kernel, but that code has a "race"
+	 * when the normal REBOOT IPI times out and NMIs are sent to
+	 * remote CPUs to stop them.  Doing WBINVD in stop_this_cpu()
+	 * could potentially increase the possibility of the "race".
+	 */
+	tdx_cpu_flush_cache();
 }
 
 #define TDX_SEAMCALL_RETRIES 10000
diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index 3ea6f587c81a..c26e2e07ff6b 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -1870,3 +1870,15 @@ u64 tdh_phymem_page_wbinvd_hkid(u64 hkid, struct page *page)
 	return seamcall(TDH_PHYMEM_PAGE_WBINVD, &args);
 }
 EXPORT_SYMBOL_GPL(tdh_phymem_page_wbinvd_hkid);
+
+void tdx_cpu_flush_cache(void)
+{
+	lockdep_assert_preemption_disabled();
+
+	if (!this_cpu_read(cache_state_incoherent))
+		return;
+
+	wbinvd();
+	this_cpu_write(cache_state_incoherent, false);
+}
+EXPORT_SYMBOL_GPL(tdx_cpu_flush_cache);
-- 
2.50.1

Re: [PATCH v6 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

[Sean Christopherson]

On Thu, Aug 14, 2025, Kai Huang wrote:
>  arch/x86/include/asm/tdx.h  |  2 ++
>  arch/x86/kvm/vmx/tdx.c      | 12 ++++++++++++
>  arch/x86/virt/vmx/tdx/tdx.c | 12 ++++++++++++
>  3 files changed, 26 insertions(+)
> 
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index 0922265c6bdc..e9a213582f03 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -217,6 +217,7 @@ u64 tdh_mem_page_remove(struct tdx_td *td, u64 gpa, u64 level, u64 *ext_err1, u6
>  u64 tdh_phymem_cache_wb(bool resume);
>  u64 tdh_phymem_page_wbinvd_tdr(struct tdx_td *td);
>  u64 tdh_phymem_page_wbinvd_hkid(u64 hkid, struct page *page);
> +void tdx_cpu_flush_cache(void);
>  #else
>  static inline void tdx_init(void) { }
>  static inline int tdx_cpu_enable(void) { return -ENODEV; }
> @@ -224,6 +225,7 @@ static inline int tdx_enable(void)  { return -ENODEV; }
>  static inline u32 tdx_get_nr_guest_keyids(void) { return 0; }
>  static inline const char *tdx_dump_mce_info(struct mce *m) { return NULL; }
>  static inline const struct tdx_sys_info *tdx_get_sysinfo(void) { return NULL; }
> +static inline void tdx_cpu_flush_cache(void) { }

Stub is unnecessary.  tdx.c is built iff KVM_INTEL_TDX=y, and that depends on
INTEL_TDX_HOST.

At a glance, some of the existing stubs are useless as well.

>  #endif	/* CONFIG_INTEL_TDX_HOST */
>  
>  #endif /* !__ASSEMBLER__ */
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 66744f5768c8..1bc6f52e0cd7 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -442,6 +442,18 @@ void tdx_disable_virtualization_cpu(void)
>  		tdx_flush_vp(&arg);
>  	}
>  	local_irq_restore(flags);
> +
> +	/*
> +	 * No more TDX activity on this CPU from here.  Flush cache to
> +	 * avoid having to do WBINVD in stop_this_cpu() during kexec.
> +	 *
> +	 * Kexec calls native_stop_other_cpus() to stop remote CPUs
> +	 * before booting to new kernel, but that code has a "race"
> +	 * when the normal REBOOT IPI times out and NMIs are sent to
> +	 * remote CPUs to stop them.  Doing WBINVD in stop_this_cpu()
> +	 * could potentially increase the possibility of the "race".
> +	 */
> +	tdx_cpu_flush_cache();

IIUC, this can be:

	if (IS_ENABLED(CONFIG_KEXEC))
		tdx_cpu_flush_cache();

>  }
>  
>  #define TDX_SEAMCALL_RETRIES 10000
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index 3ea6f587c81a..c26e2e07ff6b 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -1870,3 +1870,15 @@ u64 tdh_phymem_page_wbinvd_hkid(u64 hkid, struct page *page)
>  	return seamcall(TDH_PHYMEM_PAGE_WBINVD, &args);
>  }
>  EXPORT_SYMBOL_GPL(tdh_phymem_page_wbinvd_hkid);
> +
> +void tdx_cpu_flush_cache(void)
> +{
> +	lockdep_assert_preemption_disabled();
> +
> +	if (!this_cpu_read(cache_state_incoherent))
> +		return;
> +
> +	wbinvd();
> +	this_cpu_write(cache_state_incoherent, false);
> +}
> +EXPORT_SYMBOL_GPL(tdx_cpu_flush_cache);
> -- 
> 2.50.1
> 

Re: [PATCH v6 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

[Edgecombe, Rick P]

On Thu, 2025-08-14 at 06:54 -0700, Sean Christopherson wrote:
> >   static inline void tdx_init(void) { }
> >   static inline int tdx_cpu_enable(void) { return -ENODEV; }
> > @@ -224,6 +225,7 @@ static inline int tdx_enable(void)  { return -ENODEV; }
> >   static inline u32 tdx_get_nr_guest_keyids(void) { return 0; }
> >   static inline const char *tdx_dump_mce_info(struct mce *m) { return NULL;
> > }
> >   static inline const struct tdx_sys_info *tdx_get_sysinfo(void) { return
> > NULL; }
> > +static inline void tdx_cpu_flush_cache(void) { }
> 
> Stub is unnecessary.  tdx.c is built iff KVM_INTEL_TDX=y, and that depends on
> INTEL_TDX_HOST.
> 
> At a glance, some of the existing stubs are useless as well.

Oh, yep. We'll add it to the cleanup list.

> 
> >   #endif	/* CONFIG_INTEL_TDX_HOST */
> >   
> >   #endif /* !__ASSEMBLER__ */
> > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> > index 66744f5768c8..1bc6f52e0cd7 100644
> > --- a/arch/x86/kvm/vmx/tdx.c
> > +++ b/arch/x86/kvm/vmx/tdx.c
> > @@ -442,6 +442,18 @@ void tdx_disable_virtualization_cpu(void)
> >   		tdx_flush_vp(&arg);
> >   	}
> >   	local_irq_restore(flags);
> > +
> > +	/*
> > +	 * No more TDX activity on this CPU from here.  Flush cache to
> > +	 * avoid having to do WBINVD in stop_this_cpu() during kexec.
> > +	 *
> > +	 * Kexec calls native_stop_other_cpus() to stop remote CPUs
> > +	 * before booting to new kernel, but that code has a "race"
> > +	 * when the normal REBOOT IPI times out and NMIs are sent to
> > +	 * remote CPUs to stop them.  Doing WBINVD in stop_this_cpu()
> > +	 * could potentially increase the possibility of the "race".
> > +	 */
> > +	tdx_cpu_flush_cache();
> 
> IIUC, this can be:
> 
> 	if (IS_ENABLED(CONFIG_KEXEC))
> 		tdx_cpu_flush_cache();
> 

No strong objection, just 2 cents. I bet !CONFIG_KEXEC && CONFIG_INTEL_TDX_HOST
kernels will be the minority. Seems like an opportunity to simplify the code.

But if we do this, we should probably compile out the unused
tdx_cpu_flush_cache() too.

> >   }
> >  

Re: [PATCH v6 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

[Sean Christopherson]

On Thu, Aug 14, 2025, Rick P Edgecombe wrote:
> On Thu, 2025-08-14 at 06:54 -0700, Sean Christopherson wrote:
> > > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> > > index 66744f5768c8..1bc6f52e0cd7 100644
> > > --- a/arch/x86/kvm/vmx/tdx.c
> > > +++ b/arch/x86/kvm/vmx/tdx.c
> > > @@ -442,6 +442,18 @@ void tdx_disable_virtualization_cpu(void)
> > >   		tdx_flush_vp(&arg);
> > >   	}
> > >   	local_irq_restore(flags);
> > > +
> > > +	/*
> > > +	 * No more TDX activity on this CPU from here.  Flush cache to
> > > +	 * avoid having to do WBINVD in stop_this_cpu() during kexec.
> > > +	 *
> > > +	 * Kexec calls native_stop_other_cpus() to stop remote CPUs
> > > +	 * before booting to new kernel, but that code has a "race"
> > > +	 * when the normal REBOOT IPI times out and NMIs are sent to
> > > +	 * remote CPUs to stop them.  Doing WBINVD in stop_this_cpu()
> > > +	 * could potentially increase the possibility of the "race".

Why is that race problematic?  The changelog just says

 : However, the native_stop_other_cpus() and stop_this_cpu() have a "race"
 : which is extremely rare to happen but could cause the system to hang.
 : 
 : Specifically, the native_stop_other_cpus() firstly sends normal reboot
 : IPI to remote CPUs and waits one second for them to stop.  If that times
 : out, native_stop_other_cpus() then sends NMIs to remote CPUs to stop
 : them.

without explaining how that can cause a system hang.

> > > +	 */
> > > +	tdx_cpu_flush_cache();
> > 
> > IIUC, this can be:
> > 
> > 	if (IS_ENABLED(CONFIG_KEXEC))
> > 		tdx_cpu_flush_cache();
> > 
> 
> No strong objection, just 2 cents. I bet !CONFIG_KEXEC && CONFIG_INTEL_TDX_HOST
> kernels will be the minority. Seems like an opportunity to simplify the code.

Reducing the number of lines of code is not always a simplification.  IMO, not
checking CONFIG_KEXEC adds "complexity" because anyone that reads the comment
(and/or the massive changelog) will be left wondering why there's a bunch of
documentation that talks about kexec, but no hint of kexec considerations in the
code.

Re: [PATCH v6 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

[Huang, Kai]

On Thu, 2025-08-14 at 11:00 -0700, Sean Christopherson wrote:
> On Thu, Aug 14, 2025, Rick P Edgecombe wrote:
> > On Thu, 2025-08-14 at 06:54 -0700, Sean Christopherson wrote:
> > > > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> > > > index 66744f5768c8..1bc6f52e0cd7 100644
> > > > --- a/arch/x86/kvm/vmx/tdx.c
> > > > +++ b/arch/x86/kvm/vmx/tdx.c
> > > > @@ -442,6 +442,18 @@ void tdx_disable_virtualization_cpu(void)
> > > >   		tdx_flush_vp(&arg);
> > > >   	}
> > > >   	local_irq_restore(flags);
> > > > +
> > > > +	/*
> > > > +	 * No more TDX activity on this CPU from here.  Flush cache to
> > > > +	 * avoid having to do WBINVD in stop_this_cpu() during kexec.
> > > > +	 *
> > > > +	 * Kexec calls native_stop_other_cpus() to stop remote CPUs
> > > > +	 * before booting to new kernel, but that code has a "race"
> > > > +	 * when the normal REBOOT IPI times out and NMIs are sent to
> > > > +	 * remote CPUs to stop them.  Doing WBINVD in stop_this_cpu()
> > > > +	 * could potentially increase the possibility of the "race".
> 
> Why is that race problematic?  The changelog just says
> 
>  : However, the native_stop_other_cpus() and stop_this_cpu() have a "race"
>  : which is extremely rare to happen but could cause the system to hang.
>  : even
>  : Specifically, the native_stop_other_cpus() firstly sends normal reboot
>  : IPI to remote CPUs and waits one second for them to stop.  If that times
>  : out, native_stop_other_cpus() then sends NMIs to remote CPUs to stop
>  : them.
> 
> without explaining how that can cause a system hang.

Thanks for review. Sean.

The race is about the kexec-ing CPU could jump to second kernel when other
CPUs have not fully stopped.  

In the patch 3 I appended a link in the changelog to explain the race:

https://lore.kernel.org/kvm/b963fcd60abe26c7ec5dc20b42f1a2ebbcc72397.1750934177.git.kai.huang@intel.com/

Please see "[*] The "race" in native_stop_other_cpus()" part.

I will put the link in the changelog of this patch too.

> 
> > > > +	 */
> > > > +	tdx_cpu_flush_cache();
> > > 
> > > IIUC, this can be:
> > > 
> > > 	if (IS_ENABLED(CONFIG_KEXEC))
> > > 		tdx_cpu_flush_cache();
> > > 
> > 
> > No strong objection, just 2 cents. I bet !CONFIG_KEXEC && CONFIG_INTEL_TDX_HOST
> > kernels will be the minority. Seems like an opportunity to simplify the code.
> 
> Reducing the number of lines of code is not always a simplification.  IMO, not
> checking CONFIG_KEXEC adds "complexity" because anyone that reads the comment
> (and/or the massive changelog) will be left wondering why there's a bunch of
> documentation that talks about kexec, but no hint of kexec considerations in the
> code.

I think we can use 'kexec_in_progress', which is even better than
IS_ENABLED(CONFIG_KEXEC) IMHO.

When CONFIG_KEXEC is on, 'kexec_in_progress' will only be set when kexec
is actually happening, thus tdx_cpu_flush_cache() will only be called for
kexec.  When CONFIG_KEXEC (CONFIG_KEXEC_CORE) is off, then
'kexec_in_progress' is a macro defined to false.  The compiler can
optimize this out too I suppose.

Any comments?

Re: [PATCH v6 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

[Huang, Kai]

On Thu, 2025-08-14 at 06:54 -0700, Sean Christopherson wrote:
> > diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> > index 0922265c6bdc..e9a213582f03 100644
> > --- a/arch/x86/include/asm/tdx.h
> > +++ b/arch/x86/include/asm/tdx.h
> > @@ -217,6 +217,7 @@ u64 tdh_mem_page_remove(struct tdx_td *td, u64 gpa, u64 level, u64 *ext_err1, u6
> >   u64 tdh_phymem_cache_wb(bool resume);
> >   u64 tdh_phymem_page_wbinvd_tdr(struct tdx_td *td);
> >   u64 tdh_phymem_page_wbinvd_hkid(u64 hkid, struct page *page);
> > +void tdx_cpu_flush_cache(void);
> >   #else
> >   static inline void tdx_init(void) { }
> >   static inline int tdx_cpu_enable(void) { return -ENODEV; }
> > @@ -224,6 +225,7 @@ static inline int tdx_enable(void)  { return -ENODEV; }
> >   static inline u32 tdx_get_nr_guest_keyids(void) { return 0; }
> >   static inline const char *tdx_dump_mce_info(struct mce *m) { return NULL; }
> >   static inline const struct tdx_sys_info *tdx_get_sysinfo(void) { return NULL; }
> > +static inline void tdx_cpu_flush_cache(void) { }
> 
> Stub is unnecessary.  tdx.c is built iff KVM_INTEL_TDX=y, and that depends on
> INTEL_TDX_HOST.
> 
> At a glance, some of the existing stubs are useless as well.

OK I will remove it.  Thanks.

Re: [PATCH v6 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

[Sean Christopherson]

On Thu, Aug 14, 2025, Kai Huang wrote:
> On Thu, 2025-08-14 at 11:00 -0700, Sean Christopherson wrote:
> > > > > +	 */
> > > > > +	tdx_cpu_flush_cache();
> > > > 
> > > > IIUC, this can be:
> > > > 
> > > > 	if (IS_ENABLED(CONFIG_KEXEC))
> > > > 		tdx_cpu_flush_cache();
> > > > 
> > > 
> > > No strong objection, just 2 cents. I bet !CONFIG_KEXEC && CONFIG_INTEL_TDX_HOST
> > > kernels will be the minority. Seems like an opportunity to simplify the code.
> > 
> > Reducing the number of lines of code is not always a simplification.  IMO, not
> > checking CONFIG_KEXEC adds "complexity" because anyone that reads the comment
> > (and/or the massive changelog) will be left wondering why there's a bunch of
> > documentation that talks about kexec, but no hint of kexec considerations in the
> > code.
> 
> I think we can use 'kexec_in_progress', which is even better than
> IS_ENABLED(CONFIG_KEXEC) IMHO.

I don't think that will accomplish what you want.  E.g. kvm-intel.ko is unloaded
after doing TDX things, while kexec_in_progress=false, and then some time later
a kexec is triggered.  In that case, stop_this_cpu() will still get stuck doing
WBINVD.

Re: [PATCH v6 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

[Huang, Kai]

On Thu, 2025-08-14 at 16:22 -0700, Sean Christopherson wrote:
> On Thu, Aug 14, 2025, Kai Huang wrote:
> > On Thu, 2025-08-14 at 11:00 -0700, Sean Christopherson wrote:
> > > > > > +	 */
> > > > > > +	tdx_cpu_flush_cache();
> > > > > 
> > > > > IIUC, this can be:
> > > > > 
> > > > > 	if (IS_ENABLED(CONFIG_KEXEC))
> > > > > 		tdx_cpu_flush_cache();
> > > > > 
> > > > 
> > > > No strong objection, just 2 cents. I bet !CONFIG_KEXEC && CONFIG_INTEL_TDX_HOST
> > > > kernels will be the minority. Seems like an opportunity to simplify the code.
> > > 
> > > Reducing the number of lines of code is not always a simplification.  IMO, not
> > > checking CONFIG_KEXEC adds "complexity" because anyone that reads the comment
> > > (and/or the massive changelog) will be left wondering why there's a bunch of
> > > documentation that talks about kexec, but no hint of kexec considerations in the
> > > code.
> > 
> > I think we can use 'kexec_in_progress', which is even better than
> > IS_ENABLED(CONFIG_KEXEC) IMHO.
> 
> I don't think that will accomplish what you want.  E.g. kvm-intel.ko is unloaded
> after doing TDX things, while kexec_in_progress=false, and then some time later
> a kexec is triggered.  In that case, stop_this_cpu() will still get stuck doing
> WBINVD.

Right.  Thanks.  Let me think more on this.

One minor thing is I think we should use IS_ENABLED(CONFIG_KEXEC_CORE)
instead.  Besides the CONFIG_KEXEC, there is another CONFIG_KEXEC_FILE,
and both of them select CONFIG_KEXEC_CORE.

Re: [PATCH v6 1/7] x86/kexec: Consolidate relocate_kernel() function parameters

[Borislav Petkov]

On Thu, Aug 14, 2025 at 11:59:01AM +1200, Kai Huang wrote:
> During kexec, the kernel jumps to the new kernel in relocate_kernel(),
> which is implemented in assembly and both 32-bit and 64-bit have their
> own version.
> 
> Currently, for both 32-bit and 64-bit, the last two parameters of the
> relocate_kernel() are both 'unsigned int' but actually they only convey
> a boolean, i.e., one bit information.  The 'unsigned int' has enough
> space to carry two bits information therefore there's no need to pass
> the two booleans in two separate 'unsigned int'.
> 
> Consolidate the last two function parameters of relocate_kernel() into a
> single 'unsigned int' and pass flags instead.
> 
> Only consolidate the 64-bit version albeit the similar optimization can
> be done for the 32-bit version too.  Don't bother changing the 32-bit
> version while it is working (since assembly code change is required).
> 
> Signed-off-by: Kai Huang <kai.huang@intel.com>
> Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
> 
>  v5 -> v6:
>   - Add Tom's RB.
> 
>  v4 -> v5:
>   - RELOC_KERNEL_HOST_MEM_ACTIVE -> RELOC_KERNEL_HOST_MEM_ENC_ACTIVE
>     (Tom)
>   - Add a comment to explain only RELOC_KERNEL_PRESERVE_CONTEXT is
>     restored after jumping back from peer kernel for preserved_context
>     kexec (pointed out by Tom).
>   - Use testb instead of testq when comparing the flag with R11 to save
>     3 bytes (Hpa).
> 
>  v4:
>   - new patch
> 
> 
> ---
>  arch/x86/include/asm/kexec.h         | 12 ++++++++++--
>  arch/x86/kernel/machine_kexec_64.c   | 22 +++++++++++++---------
>  arch/x86/kernel/relocate_kernel_64.S | 25 +++++++++++++++----------
>  3 files changed, 38 insertions(+), 21 deletions(-)

Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v6 1/7] x86/kexec: Consolidate relocate_kernel() function parameters

[Huang, Kai]

On Fri, 2025-08-15 at 12:46 +0200, Borislav Petkov wrote:
> On Thu, Aug 14, 2025 at 11:59:01AM +1200, Kai Huang wrote:
> > During kexec, the kernel jumps to the new kernel in relocate_kernel(),
> > which is implemented in assembly and both 32-bit and 64-bit have their
> > own version.
> > 
> > Currently, for both 32-bit and 64-bit, the last two parameters of the
> > relocate_kernel() are both 'unsigned int' but actually they only convey
> > a boolean, i.e., one bit information.  The 'unsigned int' has enough
> > space to carry two bits information therefore there's no need to pass
> > the two booleans in two separate 'unsigned int'.
> > 
> > Consolidate the last two function parameters of relocate_kernel() into a
> > single 'unsigned int' and pass flags instead.
> > 
> > Only consolidate the 64-bit version albeit the similar optimization can
> > be done for the 32-bit version too.  Don't bother changing the 32-bit
> > version while it is working (since assembly code change is required).
> > 
> > Signed-off-by: Kai Huang <kai.huang@intel.com>
> > Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
> > ---
> > 
> >  v5 -> v6:
> >   - Add Tom's RB.
> > 
> >  v4 -> v5:
> >   - RELOC_KERNEL_HOST_MEM_ACTIVE -> RELOC_KERNEL_HOST_MEM_ENC_ACTIVE
> >     (Tom)
> >   - Add a comment to explain only RELOC_KERNEL_PRESERVE_CONTEXT is
> >     restored after jumping back from peer kernel for preserved_context
> >     kexec (pointed out by Tom).
> >   - Use testb instead of testq when comparing the flag with R11 to save
> >     3 bytes (Hpa).
> > 
> >  v4:
> >   - new patch
> > 
> > 
> > ---
> >  arch/x86/include/asm/kexec.h         | 12 ++++++++++--
> >  arch/x86/kernel/machine_kexec_64.c   | 22 +++++++++++++---------
> >  arch/x86/kernel/relocate_kernel_64.S | 25 +++++++++++++++----------
> >  3 files changed, 38 insertions(+), 21 deletions(-)
> 
> Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>

Thanks Boris!

Re: [PATCH v6 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

[Paolo Bonzini]

On 8/15/25 02:00, Huang, Kai wrote:
> On Thu, 2025-08-14 at 16:22 -0700, Sean Christopherson wrote:
>> On Thu, Aug 14, 2025, Kai Huang wrote:
>>> On Thu, 2025-08-14 at 11:00 -0700, Sean Christopherson wrote:
>>>> Reducing the number of lines of code is not always a simplification.  IMO, not
>>>> checking CONFIG_KEXEC adds "complexity" because anyone that reads the comment
>>>> (and/or the massive changelog) will be left wondering why there's a bunch of
>>>> documentation that talks about kexec, but no hint of kexec considerations in the
>>>> code.
> 
> One minor thing is I think we should use IS_ENABLED(CONFIG_KEXEC_CORE)
> instead.  Besides the CONFIG_KEXEC, there is another CONFIG_KEXEC_FILE,
> and both of them select CONFIG_KEXEC_CORE.

Agreed on needing CONFIG_KEXEC_CORE if you did test it, however:

1) The big comment, explaining how this is done for kexec, makes it 
clear that this is what the WBINVD is needed for.  I don't think you'd 
be left wondering why there's no hint of kexec in the comment.

2) ... but anyway, KVM is the wrong place to do the test.  If anything, 
since we need a v7 to change the unnecessary stub, you could move that 
stub under #ifndef CONFIG_KEXEC_CORE and rename the function to 
tdx_cpu_flush_cache_for_kexec().

Paolo

Re: [PATCH v6 2/7] x86/sme: Use percpu boolean to control WBINVD during kexec

[Borislav Petkov]

On Thu, Aug 14, 2025 at 11:59:02AM +1200, Kai Huang wrote:
> TL;DR:
> 
> Prepare to unify how TDX and SME do cache flushing during kexec by
> making a percpu boolean control whether to do the WBINVD.
> 
> -- Background --
> 
> On SME platforms, dirty cacheline aliases with and without encryption
> bit can coexist, and the CPU can flush them back to memory in random
> order.  During kexec, the caches must be flushed before jumping to the
> new kernel otherwise the dirty cachelines could silently corrupt the
> memory used by the new kernel due to different encryption property.
> 
> TDX also needs a cache flush during kexec for the same reason.  It would
> be good to have a generic way to flush the cache instead of scattering
> checks for each feature all around.
> 
> When SME is enabled, the kernel basically encrypts all memory including
> the kernel itself and a simple memory write from the kernel could dirty
> cachelines.  Currently, the kernel uses WBINVD to flush the cache for
> SME during kexec in two places:
> 
> 1) the one in stop_this_cpu() for all remote CPUs when the kexec-ing CPU
>    stops them;
> 2) the one in the relocate_kernel() where the kexec-ing CPU jumps to the
>    new kernel.
> 
> -- Solution --
> 
> Unlike SME, TDX can only dirty cachelines when it is used (i.e., when
> SEAMCALLs are performed).  Since there are no more SEAMCALLs after the
> aforementioned WBINVDs, leverage this for TDX.
> 
> To unify the approach for SME and TDX, use a percpu boolean to indicate
> the cache may be in an incoherent state and needs flushing during kexec,
> and set the boolean for SME.  TDX can then leverage it.
> 
> While SME could use a global flag (since it's enabled at early boot and
> enabled on all CPUs), the percpu flag fits TDX better:
> 
> The percpu flag can be set when a CPU makes a SEAMCALL, and cleared when
> another WBINVD on the CPU obviates the need for a kexec-time WBINVD.
> Saving kexec-time WBINVD is valuable, because there is an existing
> race[*] where kexec could proceed while another CPU is active.  WBINVD
> could make this race worse, so it's worth skipping it when possible.
> 
> -- Side effect to SME --
> 
> Today the first WBINVD in the stop_this_cpu() is performed when SME is
> *supported* by the platform, and the second WBINVD is done in
> relocate_kernel() when SME is *activated* by the kernel.  Make things
> simple by changing to do the second WBINVD when the platform supports
> SME.  This allows the kernel to simply turn on this percpu boolean when
> bringing up a CPU by checking whether the platform supports SME.
> 
> No other functional change intended.
> 
> [*] The aforementioned race:
> 
> During kexec native_stop_other_cpus() is called to stop all remote CPUs
> before jumping to the new kernel.  native_stop_other_cpus() firstly
> sends normal REBOOT vector IPIs to stop remote CPUs and waits them to
> stop.  If that times out, it sends NMI to stop the CPUs that are still
> alive.  The race happens when native_stop_other_cpus() has to send NMIs
> and could potentially result in the system hang (for more information
> please see [1]).

This text is meandering a bit too much across a bunch of things and could be
made tighter... Just a nitpick anyway...

>  arch/x86/include/asm/kexec.h         |  4 ++--
>  arch/x86/include/asm/processor.h     |  2 ++
>  arch/x86/kernel/cpu/amd.c            | 17 +++++++++++++++++
>  arch/x86/kernel/machine_kexec_64.c   | 14 ++++++++++----
>  arch/x86/kernel/process.c            | 24 +++++++++++-------------
>  arch/x86/kernel/relocate_kernel_64.S | 13 ++++++++++---
>  6 files changed, 52 insertions(+), 22 deletions(-)

Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v6 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

[Huang, Kai]

On Tue, 2025-08-19 at 12:31 +0200, Paolo Bonzini wrote:
> On 8/15/25 02:00, Huang, Kai wrote:
> > On Thu, 2025-08-14 at 16:22 -0700, Sean Christopherson wrote:
> > > On Thu, Aug 14, 2025, Kai Huang wrote:
> > > > On Thu, 2025-08-14 at 11:00 -0700, Sean Christopherson wrote:
> > > > > Reducing the number of lines of code is not always a simplification.  IMO, not
> > > > > checking CONFIG_KEXEC adds "complexity" because anyone that reads the comment
> > > > > (and/or the massive changelog) will be left wondering why there's a bunch of
> > > > > documentation that talks about kexec, but no hint of kexec considerations in the
> > > > > code.
> > 
> > One minor thing is I think we should use IS_ENABLED(CONFIG_KEXEC_CORE)
> > instead.  Besides the CONFIG_KEXEC, there is another CONFIG_KEXEC_FILE,
> > and both of them select CONFIG_KEXEC_CORE.
> 
> Agreed on needing CONFIG_KEXEC_CORE if you did test it, however:
> 
> 1) The big comment, explaining how this is done for kexec, makes it 
> clear that this is what the WBINVD is needed for.  I don't think you'd 
> be left wondering why there's no hint of kexec in the comment.

(Thanks for the feedback.)

Agreed.

> 
> 2) ... but anyway, KVM is the wrong place to do the test.  If anything, 
> since we need a v7 to change the unnecessary stub, you could move that 
> stub under #ifndef CONFIG_KEXEC_CORE and rename the function to 
> tdx_cpu_flush_cache_for_kexec().
> 
> Paolo

Agreed on renaming to tdx_cpu_flush_cache_for_kexec().

But with the "for_kexec()" part in the function name, it already implies
it is related to kexec, and I kinda think there's no need to test
IS_ENABLED(CONFIG_KEXEC_CORE) anymore.

One of the main purpose of this series is to unblock TDX_HOST and KEXEC in
the Kconfig, since otherwise I've been told distros will simply choose to
disable TDX_HOST in the Kconfig.  So in reality, I suppose they will be on
together probably in like 95% cases, if not 100%.

If we want to test CONFIG_KEXEC_CORE in tdx_cpu_flush_cache_for_kexec(),
then it would be a little bit weird that why we don't test it in other
places, e.g., when setting up the boolean.  Testing it in all places would
make the code unnecessarily long and harder to read.

So my preference is to simply rename to tdx_cpu_flush_cache_for_kexec().

Paolo/Sean, are you OK with this?

Re: [PATCH v6 2/7] x86/sme: Use percpu boolean to control WBINVD during kexec

[Huang, Kai]

On Tue, 2025-08-19 at 21:28 +0200, Borislav Petkov wrote:
> On Thu, Aug 14, 2025 at 11:59:02AM +1200, Kai Huang wrote:
> > TL;DR:
> > 
> > Prepare to unify how TDX and SME do cache flushing during kexec by
> > making a percpu boolean control whether to do the WBINVD.
> > 
> > -- Background --
> > 
> > On SME platforms, dirty cacheline aliases with and without encryption
> > bit can coexist, and the CPU can flush them back to memory in random
> > order.  During kexec, the caches must be flushed before jumping to the
> > new kernel otherwise the dirty cachelines could silently corrupt the
> > memory used by the new kernel due to different encryption property.
> > 
> > TDX also needs a cache flush during kexec for the same reason.  It would
> > be good to have a generic way to flush the cache instead of scattering
> > checks for each feature all around.
> > 
> > When SME is enabled, the kernel basically encrypts all memory including
> > the kernel itself and a simple memory write from the kernel could dirty
> > cachelines.  Currently, the kernel uses WBINVD to flush the cache for
> > SME during kexec in two places:
> > 
> > 1) the one in stop_this_cpu() for all remote CPUs when the kexec-ing CPU
> >    stops them;
> > 2) the one in the relocate_kernel() where the kexec-ing CPU jumps to the
> >    new kernel.
> > 
> > -- Solution --
> > 
> > Unlike SME, TDX can only dirty cachelines when it is used (i.e., when
> > SEAMCALLs are performed).  Since there are no more SEAMCALLs after the
> > aforementioned WBINVDs, leverage this for TDX.
> > 
> > To unify the approach for SME and TDX, use a percpu boolean to indicate
> > the cache may be in an incoherent state and needs flushing during kexec,
> > and set the boolean for SME.  TDX can then leverage it.
> > 
> > While SME could use a global flag (since it's enabled at early boot and
> > enabled on all CPUs), the percpu flag fits TDX better:
> > 
> > The percpu flag can be set when a CPU makes a SEAMCALL, and cleared when
> > another WBINVD on the CPU obviates the need for a kexec-time WBINVD.
> > Saving kexec-time WBINVD is valuable, because there is an existing
> > race[*] where kexec could proceed while another CPU is active.  WBINVD
> > could make this race worse, so it's worth skipping it when possible.
> > 
> > -- Side effect to SME --
> > 
> > Today the first WBINVD in the stop_this_cpu() is performed when SME is
> > *supported* by the platform, and the second WBINVD is done in
> > relocate_kernel() when SME is *activated* by the kernel.  Make things
> > simple by changing to do the second WBINVD when the platform supports
> > SME.  This allows the kernel to simply turn on this percpu boolean when
> > bringing up a CPU by checking whether the platform supports SME.
> > 
> > No other functional change intended.
> > 
> > [*] The aforementioned race:
> > 
> > During kexec native_stop_other_cpus() is called to stop all remote CPUs
> > before jumping to the new kernel.  native_stop_other_cpus() firstly
> > sends normal REBOOT vector IPIs to stop remote CPUs and waits them to
> > stop.  If that times out, it sends NMI to stop the CPUs that are still
> > alive.  The race happens when native_stop_other_cpus() has to send NMIs
> > and could potentially result in the system hang (for more information
> > please see [1]).
> 
> This text is meandering a bit too much across a bunch of things and could be
> made tighter... Just a nitpick anyway...

Yeah agreed.  I've worked to improve it but ... :-)

I'll keep this in mind and do better in the future!

> 
> >  arch/x86/include/asm/kexec.h         |  4 ++--
> >  arch/x86/include/asm/processor.h     |  2 ++
> >  arch/x86/kernel/cpu/amd.c            | 17 +++++++++++++++++
> >  arch/x86/kernel/machine_kexec_64.c   | 14 ++++++++++----
> >  arch/x86/kernel/process.c            | 24 +++++++++++-------------
> >  arch/x86/kernel/relocate_kernel_64.S | 13 ++++++++++---
> >  6 files changed, 52 insertions(+), 22 deletions(-)
> 
> Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>

Thanks!

Re: [PATCH v6 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

[Paolo Bonzini]

On 8/19/25 23:53, Huang, Kai wrote:
> On Tue, 2025-08-19 at 12:31 +0200, Paolo Bonzini wrote:
>> 2) ... but anyway, KVM is the wrong place to do the test.  If anything,
>> since we need a v7 to change the unnecessary stub, you could move that
>> stub under #ifndef CONFIG_KEXEC_CORE and rename the function to
>> tdx_cpu_flush_cache_for_kexec().
> 
> Agreed on renaming to tdx_cpu_flush_cache_for_kexec().
> 
> But with the "for_kexec()" part in the function name, it already implies
> it is related to kexec, and I kinda think there's no need to test
> IS_ENABLED(CONFIG_KEXEC_CORE) anymore.
> 
> One of the main purpose of this series is to unblock TDX_HOST and KEXEC in
> the Kconfig, since otherwise I've been told distros will simply choose to
> disable TDX_HOST in the Kconfig.  So in reality, I suppose they will be on
> together probably in like 95% cases, if not 100%.
> 
> If we want to test CONFIG_KEXEC_CORE in tdx_cpu_flush_cache_for_kexec(),
> then it would be a little bit weird that why we don't test it in other
> places, e.g., when setting up the boolean.  Testing it in all places would
> make the code unnecessarily long and harder to read.

No I don't mean testing it there, but just making
tdx_cpu_flush_cache_for_kexec() a stub when CONFIG_KEXEC_CORE is
undefined:

diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index e9a213582f03..913199b1954b 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -217,7 +217,6 @@ u64 tdh_mem_page_remove(struct tdx_td *td, u64 gpa, u64 level, u64 *ext_err1, u6
  u64 tdh_phymem_cache_wb(bool resume);
  u64 tdh_phymem_page_wbinvd_tdr(struct tdx_td *td);
  u64 tdh_phymem_page_wbinvd_hkid(u64 hkid, struct page *page);
-void tdx_cpu_flush_cache(void);
  #else
  static inline void tdx_init(void) { }
  static inline int tdx_cpu_enable(void) { return -ENODEV; }
@@ -225,8 +224,13 @@ static inline int tdx_enable(void)  { return -ENODEV; }
  static inline u32 tdx_get_nr_guest_keyids(void) { return 0; }
  static inline const char *tdx_dump_mce_info(struct mce *m) { return NULL; }
  static inline const struct tdx_sys_info *tdx_get_sysinfo(void) { return NULL; }
-static inline void tdx_cpu_flush_cache(void) { }
  #endif	/* CONFIG_INTEL_TDX_HOST */
  
+#ifdef CONFIG_KEXEC_CORE
+void tdx_cpu_flush_cache_for_kexec(void);
+#else
+static inline void tdx_cpu_flush_cache_for_kexec(void) { }
+#endif
+
  #endif /* !__ASSEMBLER__ */
  #endif /* _ASM_X86_TDX_H */
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 93477233baae..376d49ef4472 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -453,7 +453,7 @@ void tdx_disable_virtualization_cpu(void)
  	 * remote CPUs to stop them.  Doing WBINVD in stop_this_cpu()
  	 * could potentially increase the possibility of the "race".
  	 */
-	tdx_cpu_flush_cache();
+	tdx_cpu_flush_cache_for_kexec();
  }
  
  #define TDX_SEAMCALL_RETRIES 10000
diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index c26e2e07ff6b..cd2a36dbbfc5 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -1871,7 +1871,7 @@ u64 tdh_phymem_page_wbinvd_hkid(u64 hkid, struct page *page)
  }
  EXPORT_SYMBOL_GPL(tdh_phymem_page_wbinvd_hkid);
  
-void tdx_cpu_flush_cache(void)
+void tdx_cpu_flush_cache_for_kexec(void)
  {
  	lockdep_assert_preemption_disabled();
  
@@ -1881,4 +1881,4 @@ void tdx_cpu_flush_cache(void)
  	wbinvd();
  	this_cpu_write(cache_state_incoherent, false);
  }
-EXPORT_SYMBOL_GPL(tdx_cpu_flush_cache);
+EXPORT_SYMBOL_GPL(tdx_cpu_flush_cache_for_kexec);


Personally, I'm totally okay with v6.  But the above change seems
to me like the best way to obey Sean's objection, better than
adding the test in KVM.

Paolo

Re: [PATCH v6 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

[Huang, Kai]

On Wed, 2025-08-20 at 11:51 +0200, Paolo Bonzini wrote:
> On 8/19/25 23:53, Huang, Kai wrote:
> > On Tue, 2025-08-19 at 12:31 +0200, Paolo Bonzini wrote:
> > > 2) ... but anyway, KVM is the wrong place to do the test.  If anything,
> > > since we need a v7 to change the unnecessary stub, you could move that
> > > stub under #ifndef CONFIG_KEXEC_CORE and rename the function to
> > > tdx_cpu_flush_cache_for_kexec().
> > 
> > Agreed on renaming to tdx_cpu_flush_cache_for_kexec().
> > 
> > But with the "for_kexec()" part in the function name, it already implies
> > it is related to kexec, and I kinda think there's no need to test
> > IS_ENABLED(CONFIG_KEXEC_CORE) anymore.
> > 
> > One of the main purpose of this series is to unblock TDX_HOST and KEXEC in
> > the Kconfig, since otherwise I've been told distros will simply choose to
> > disable TDX_HOST in the Kconfig.  So in reality, I suppose they will be on
> > together probably in like 95% cases, if not 100%.
> > 
> > If we want to test CONFIG_KEXEC_CORE in tdx_cpu_flush_cache_for_kexec(),
> > then it would be a little bit weird that why we don't test it in other
> > places, e.g., when setting up the boolean.  Testing it in all places would
> > make the code unnecessarily long and harder to read.
> 
> No I don't mean testing it there, but just making
> tdx_cpu_flush_cache_for_kexec() a stub when CONFIG_KEXEC_CORE is
> undefined:
> 
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index e9a213582f03..913199b1954b 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -217,7 +217,6 @@ u64 tdh_mem_page_remove(struct tdx_td *td, u64 gpa, u64 level, u64 *ext_err1, u6
>   u64 tdh_phymem_cache_wb(bool resume);
>   u64 tdh_phymem_page_wbinvd_tdr(struct tdx_td *td);
>   u64 tdh_phymem_page_wbinvd_hkid(u64 hkid, struct page *page);
> -void tdx_cpu_flush_cache(void);
>   #else
>   static inline void tdx_init(void) { }
>   static inline int tdx_cpu_enable(void) { return -ENODEV; }
> @@ -225,8 +224,13 @@ static inline int tdx_enable(void)  { return -ENODEV; }
>   static inline u32 tdx_get_nr_guest_keyids(void) { return 0; }
>   static inline const char *tdx_dump_mce_info(struct mce *m) { return NULL; }
>   static inline const struct tdx_sys_info *tdx_get_sysinfo(void) { return NULL; }
> -static inline void tdx_cpu_flush_cache(void) { }
>   #endif	/* CONFIG_INTEL_TDX_HOST */
>   
> +#ifdef CONFIG_KEXEC_CORE
> +void tdx_cpu_flush_cache_for_kexec(void);
> +#else
> +static inline void tdx_cpu_flush_cache_for_kexec(void) { }
> +#endif
> +

I think one minor issue here is, when CONFIG_INTEL_TDX_HOST is off but
CONFIG_KEXEC_CORE is on, there will be no implementation of
tdx_cpu_flush_cache_for_kexec().  This won't result in build error,
though, because when TDX_HOST is off, KVM_INTEL_TDX will be off too, i.e.,
there won't be any caller of tdx_cpu_flush_cache_for_kexec().

But this still doesn't look nice?

Btw, the above will provide the stub function when both KEXEC_CORE and
TDX_HOST is off, which seems to be a step back too?

:-)

To me, it's more straightforward to just rename it to
tdx_cpu_flush_cache_for_kexec() and remove the stub:

diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index e9a213582f03..5e37ae1a40e8 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -217,7 +217,7 @@ u64 tdh_mem_page_remove(struct tdx_td *td, u64 gpa,
u64 level, u64 *ext_err1, u6
 u64 tdh_phymem_cache_wb(bool resume);
 u64 tdh_phymem_page_wbinvd_tdr(struct tdx_td *td);
 u64 tdh_phymem_page_wbinvd_hkid(u64 hkid, struct page *page);
-void tdx_cpu_flush_cache(void);
+void tdx_cpu_flush_cache_for_kexec(void);
 #else
 static inline void tdx_init(void) { }
 static inline int tdx_cpu_enable(void) { return -ENODEV; }
@@ -225,7 +225,6 @@ static inline int tdx_enable(void)  { return -ENODEV;
}
 static inline u32 tdx_get_nr_guest_keyids(void) { return 0; }
 static inline const char *tdx_dump_mce_info(struct mce *m) { return NULL;
}
 static inline const struct tdx_sys_info *tdx_get_sysinfo(void) { return
NULL; }
-static inline void tdx_cpu_flush_cache(void) { }
 #endif /* CONFIG_INTEL_TDX_HOST */
 
 #endif /* !__ASSEMBLER__ */
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 1bc6f52e0cd7..382792e31f32 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -453,7 +453,7 @@ void tdx_disable_virtualization_cpu(void)
         * remote CPUs to stop them.  Doing WBINVD in stop_this_cpu()
         * could potentially increase the possibility of the "race".
         */
-       tdx_cpu_flush_cache();
+       tdx_cpu_flush_cache_for_kexec();
 }
 
 #define TDX_SEAMCALL_RETRIES 10000
diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index c26e2e07ff6b..cd2a36dbbfc5 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -1871,7 +1871,7 @@ u64 tdh_phymem_page_wbinvd_hkid(u64 hkid, struct
page *page)
 }
 EXPORT_SYMBOL_GPL(tdh_phymem_page_wbinvd_hkid);
 
-void tdx_cpu_flush_cache(void)
+void tdx_cpu_flush_cache_for_kexec(void)
 {
        lockdep_assert_preemption_disabled();
 
@@ -1881,4 +1881,4 @@ void tdx_cpu_flush_cache(void)
        wbinvd();
        this_cpu_write(cache_state_incoherent, false);
 }
-EXPORT_SYMBOL_GPL(tdx_cpu_flush_cache);
+EXPORT_SYMBOL_GPL(tdx_cpu_flush_cache_for_kexec);

Re: [PATCH v6 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

[Paolo Bonzini]

On 8/19/25 23:53, Huang, Kai wrote:
> If we want to test CONFIG_KEXEC_CORE in tdx_cpu_flush_cache_for_kexec(),
> then it would be a little bit weird that why we don't test it in other
> places, e.g., when setting up the boolean.  Testing it in all places would
> make the code unnecessarily long and harder to read.

I agree about not checking everywhere.  But I think this is a good
compromise too if v6 is not acceptable as is (and as far as I am
concerned, it would be):

diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index e9a213582f03..913199b1954b 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -217,7 +217,6 @@ u64 tdh_mem_page_remove(struct tdx_td *td, u64 gpa, u64 level, u64 *ext_err1, u6
  u64 tdh_phymem_cache_wb(bool resume);
  u64 tdh_phymem_page_wbinvd_tdr(struct tdx_td *td);
  u64 tdh_phymem_page_wbinvd_hkid(u64 hkid, struct page *page);
-void tdx_cpu_flush_cache(void);
  #else
  static inline void tdx_init(void) { }
  static inline int tdx_cpu_enable(void) { return -ENODEV; }
@@ -225,8 +224,13 @@ static inline int tdx_enable(void)  { return -ENODEV; }
  static inline u32 tdx_get_nr_guest_keyids(void) { return 0; }
  static inline const char *tdx_dump_mce_info(struct mce *m) { return NULL; }
  static inline const struct tdx_sys_info *tdx_get_sysinfo(void) { return NULL; }
-static inline void tdx_cpu_flush_cache(void) { }
  #endif	/* CONFIG_INTEL_TDX_HOST */
  
+#ifdef CONFIG_KEXEC_CORE
+void tdx_cpu_flush_cache_for_kexec(void);
+#else
+static inline void tdx_cpu_flush_cache_for_kexec(void) { }
+#endif
+
  #endif /* !__ASSEMBLER__ */
  #endif /* _ASM_X86_TDX_H */
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 93477233baae..376d49ef4472 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -453,7 +453,7 @@ void tdx_disable_virtualization_cpu(void)
  	 * remote CPUs to stop them.  Doing WBINVD in stop_this_cpu()
  	 * could potentially increase the possibility of the "race".
  	 */
-	tdx_cpu_flush_cache();
+	tdx_cpu_flush_cache_for_kexec();
  }
  
  #define TDX_SEAMCALL_RETRIES 10000
diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index c26e2e07ff6b..cd2a36dbbfc5 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -1871,7 +1871,8 @@ u64 tdh_phymem_page_wbinvd_hkid(u64 hkid, struct page *page)
  }
  EXPORT_SYMBOL_GPL(tdh_phymem_page_wbinvd_hkid);
  
-void tdx_cpu_flush_cache(void)
+#ifdef CONFIG_KEXEC_CORE
+void tdx_cpu_flush_cache_for_kexec(void)
  {
  	lockdep_assert_preemption_disabled();
  
@@ -1881,4 +1881,5 @@ void tdx_cpu_flush_cache(void)
  	wbinvd();
  	this_cpu_write(cache_state_incoherent, false);
  }
-EXPORT_SYMBOL_GPL(tdx_cpu_flush_cache);
+EXPORT_SYMBOL_GPL(tdx_cpu_flush_cache_for_kexec);
+#endif


It solves pretty much all the objections that Sean had, in one fell
swoop.  The name clearly references kexec, it's stubbed out if not
in use, and it's not anymore unnecessarily under CONFIG_INTEL_TDX_HOST.

Paolo

Re: [PATCH v6 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

[Paolo Bonzini]

On Wed, Aug 20, 2025 at 1:22 PM Huang, Kai <kai.huang@intel.com> wrote:
> I think one minor issue here is, when CONFIG_INTEL_TDX_HOST is off but
> CONFIG_KEXEC_CORE is on, there will be no implementation of
> tdx_cpu_flush_cache_for_kexec().  This won't result in build error,
> though, because when TDX_HOST is off, KVM_INTEL_TDX will be off too, i.e.,
> there won't be any caller of tdx_cpu_flush_cache_for_kexec().
>
> But this still doesn't look nice?

Why do you need one? It's called tdx_cpu_flush_cache_for_kexec(), you
don't need it if TDX is disabled.

> Btw, the above will provide the stub function when both KEXEC_CORE and
> TDX_HOST is off, which seems to be a step back too?

Let's just stop here. Are we really wasting this much time discussing
like 30 characters and 0 bytes of object code?

> To me, it's more straightforward to just rename it to
> tdx_cpu_flush_cache_for_kexec() and remove the stub:

Sure, just rename the function and let's call it a day. If it was me,
v6 was good enough.

Paolo

Re: [PATCH v6 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs

[Huang, Kai]

On Wed, 2025-08-20 at 22:35 +0200, Paolo Bonzini wrote:
> On Wed, Aug 20, 2025 at 1:22 PM Huang, Kai <kai.huang@intel.com> wrote:
> > I think one minor issue here is, when CONFIG_INTEL_TDX_HOST is off but
> > CONFIG_KEXEC_CORE is on, there will be no implementation of
> > tdx_cpu_flush_cache_for_kexec().  This won't result in build error,
> > though, because when TDX_HOST is off, KVM_INTEL_TDX will be off too, i.e.,
> > there won't be any caller of tdx_cpu_flush_cache_for_kexec().
> > 
> > But this still doesn't look nice?
> 
> Why do you need one? It's called tdx_cpu_flush_cache_for_kexec(), you
> don't need it if TDX is disabled.

Sorry I meant the declaration will still be there w/o the function body.

> 
> > Btw, the above will provide the stub function when both KEXEC_CORE and
> > TDX_HOST is off, which seems to be a step back too?
> 
> Let's just stop here. Are we really wasting this much time discussing
> like 30 characters and 0 bytes of object code?
> 
> > To me, it's more straightforward to just rename it to
> > tdx_cpu_flush_cache_for_kexec() and remove the stub:
> 
> Sure, just rename the function and let's call it a day. If it was me,
> v6 was good enough.
> 

Thanks for your time Paolo!