[PATCH 01/11] KVM: x86: use a separate asm-offsets.c file

[PATCH 01/11] KVM: x86: use a separate asm-offsets.c file

[Paolo Bonzini]

This already removes the ugly #includes from asm-offsets.c, but especially
it avoids a future error when asm-offsets will try to include svm/svm.h.

This would not work for kernel/asm-offsets.c, because svm/svm.h
includes kvm_cache_regs.h which is not in the include path when
compiling asm-offsets.c.  The problem is not there if the .c file is
in arch/x86/kvm.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: stable@vger.kernel.org
Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kernel/asm-offsets.c  |  6 ------
 arch/x86/kvm/.gitignore        |  2 ++
 arch/x86/kvm/Makefile          |  9 +++++++++
 arch/x86/kvm/kvm-asm-offsets.c | 18 ++++++++++++++++++
 arch/x86/kvm/vmx/vmenter.S     |  2 +-
 5 files changed, 30 insertions(+), 7 deletions(-)
 create mode 100644 arch/x86/kvm/.gitignore
 create mode 100644 arch/x86/kvm/kvm-asm-offsets.c

diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index cb50589a7102..437308004ef2 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -19,7 +19,6 @@
 #include <asm/suspend.h>
 #include <asm/tlbflush.h>
 #include <asm/tdx.h>
-#include "../kvm/vmx/vmx.h"
 
 #ifdef CONFIG_XEN
 #include <xen/interface/xen.h>
@@ -108,9 +107,4 @@ static void __used common(void)
 	OFFSET(TSS_sp0, tss_struct, x86_tss.sp0);
 	OFFSET(TSS_sp1, tss_struct, x86_tss.sp1);
 	OFFSET(TSS_sp2, tss_struct, x86_tss.sp2);
-
-	if (IS_ENABLED(CONFIG_KVM_INTEL)) {
-		BLANK();
-		OFFSET(VMX_spec_ctrl, vcpu_vmx, spec_ctrl);
-	}
 }
diff --git a/arch/x86/kvm/.gitignore b/arch/x86/kvm/.gitignore
new file mode 100644
index 000000000000..615d6ff35c00
--- /dev/null
+++ b/arch/x86/kvm/.gitignore
@@ -0,0 +1,2 @@
+/kvm-asm-offsets.s
+/kvm-asm-offsets.h
diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
index 30f244b64523..a02cf9baacc8 100644
--- a/arch/x86/kvm/Makefile
+++ b/arch/x86/kvm/Makefile
@@ -34,3 +34,12 @@ endif
 obj-$(CONFIG_KVM)	+= kvm.o
 obj-$(CONFIG_KVM_INTEL)	+= kvm-intel.o
 obj-$(CONFIG_KVM_AMD)	+= kvm-amd.o
+
+AFLAGS_vmx/vmenter.o    := -iquote $(obj)
+$(obj)/vmx/vmenter.o: $(obj)/kvm-asm-offsets.h
+
+$(obj)/kvm-asm-offsets.h: $(obj)/kvm-asm-offsets.s FORCE
+	$(call filechk,offsets,__KVM_ASM_OFFSETS_H__)
+
+targets += kvm-asm-offsets.s
+clean-files += kvm-asm-offsets.h
diff --git a/arch/x86/kvm/kvm-asm-offsets.c b/arch/x86/kvm/kvm-asm-offsets.c
new file mode 100644
index 000000000000..9d84f2b32d7f
--- /dev/null
+++ b/arch/x86/kvm/kvm-asm-offsets.c
@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Generate definitions needed by assembly language modules.
+ * This code generates raw asm output which is post-processed to extract
+ * and format the required data.
+ */
+#define COMPILE_OFFSETS
+
+#include <linux/kbuild.h>
+#include "vmx/vmx.h"
+
+static void __used common(void)
+{
+	if (IS_ENABLED(CONFIG_KVM_INTEL)) {
+		BLANK();
+		OFFSET(VMX_spec_ctrl, vcpu_vmx, spec_ctrl);
+	}
+}
diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S
index 8477d8bdd69c..0b5db4de4d09 100644
--- a/arch/x86/kvm/vmx/vmenter.S
+++ b/arch/x86/kvm/vmx/vmenter.S
@@ -1,12 +1,12 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 #include <linux/linkage.h>
 #include <asm/asm.h>
-#include <asm/asm-offsets.h>
 #include <asm/bitsperlong.h>
 #include <asm/kvm_vcpu_regs.h>
 #include <asm/nospec-branch.h>
 #include <asm/percpu.h>
 #include <asm/segment.h>
+#include "kvm-asm-offsets.h"
 #include "run_flags.h"
 
 #define WORD_SIZE (BITS_PER_LONG / 8)
-- 
2.31.1

Re: [PATCH 01/11] KVM: x86: use a separate asm-offsets.c file

[Sean Christopherson]

On Wed, Nov 09, 2022, Paolo Bonzini wrote:
> This already removes the ugly #includes from asm-offsets.c, but especially
> it avoids a future error when asm-offsets will try to include svm/svm.h.
> 
> This would not work for kernel/asm-offsets.c, because svm/svm.h
> includes kvm_cache_regs.h which is not in the include path when
> compiling asm-offsets.c.  The problem is not there if the .c file is
> in arch/x86/kvm.
> 
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Cc: stable@vger.kernel.org
> Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@google.com>

> diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S
> index 8477d8bdd69c..0b5db4de4d09 100644
> --- a/arch/x86/kvm/vmx/vmenter.S
> +++ b/arch/x86/kvm/vmx/vmenter.S
> @@ -1,12 +1,12 @@
>  /* SPDX-License-Identifier: GPL-2.0 */
>  #include <linux/linkage.h>
>  #include <asm/asm.h>
> -#include <asm/asm-offsets.h>
>  #include <asm/bitsperlong.h>
>  #include <asm/kvm_vcpu_regs.h>
>  #include <asm/nospec-branch.h>
>  #include <asm/percpu.h>
>  #include <asm/segment.h>
> +#include "kvm-asm-offsets.h"

Do you have a preference on KVM files using dashes or underscores?  Outside of
kvm-x86-ops.h and kvm-x86-pmu-ops.h, KVM x86 uses underscores.  I actually prefer
dashes because they're slightly easier to type, but when there are only a few
outliers I constantly mistype the names.  If dashes are generally, maybe we could
gradually/opportunistically move in that direction?

[PATCH 02/11] KVM: SVM: replace regs argument of __svm_vcpu_run with vcpu_svm

[Paolo Bonzini]

Since registers are reachable through vcpu_svm, and we will
need to access more fields of that struct, pass it instead
of the regs[] array.

No functional change intended.

Cc: stable@vger.kernel.org
Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/Makefile          |  3 +++
 arch/x86/kvm/kvm-asm-offsets.c |  6 ++++++
 arch/x86/kvm/svm/svm.c         |  2 +-
 arch/x86/kvm/svm/svm.h         |  2 +-
 arch/x86/kvm/svm/vmenter.S     | 37 +++++++++++++++++-----------------
 5 files changed, 30 insertions(+), 20 deletions(-)

diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
index a02cf9baacc8..f453a0f96e24 100644
--- a/arch/x86/kvm/Makefile
+++ b/arch/x86/kvm/Makefile
@@ -35,6 +35,9 @@ obj-$(CONFIG_KVM)	+= kvm.o
 obj-$(CONFIG_KVM_INTEL)	+= kvm-intel.o
 obj-$(CONFIG_KVM_AMD)	+= kvm-amd.o
 
+AFLAGS_svm/vmenter.o    := -iquote $(obj)
+$(obj)/svm/vmenter.o: $(obj)/kvm-asm-offsets.h
+
 AFLAGS_vmx/vmenter.o    := -iquote $(obj)
 $(obj)/vmx/vmenter.o: $(obj)/kvm-asm-offsets.h
 
diff --git a/arch/x86/kvm/kvm-asm-offsets.c b/arch/x86/kvm/kvm-asm-offsets.c
index 9d84f2b32d7f..30db96852e2d 100644
--- a/arch/x86/kvm/kvm-asm-offsets.c
+++ b/arch/x86/kvm/kvm-asm-offsets.c
@@ -8,9 +8,15 @@
 
 #include <linux/kbuild.h>
 #include "vmx/vmx.h"
+#include "svm/svm.h"
 
 static void __used common(void)
 {
+	if (IS_ENABLED(CONFIG_KVM_AMD)) {
+		BLANK();
+		OFFSET(SVM_vcpu_arch_regs, vcpu_svm, vcpu.arch.regs);
+	}
+
 	if (IS_ENABLED(CONFIG_KVM_INTEL)) {
 		BLANK();
 		OFFSET(VMX_spec_ctrl, vcpu_vmx, spec_ctrl);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 58f0077d9357..b412bc5773c5 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3930,7 +3930,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
 		 * vmcb02 when switching vmcbs for nested virtualization.
 		 */
 		vmload(svm->vmcb01.pa);
-		__svm_vcpu_run(vmcb_pa, (unsigned long *)&vcpu->arch.regs);
+		__svm_vcpu_run(vmcb_pa, svm);
 		vmsave(svm->vmcb01.pa);
 
 		vmload(__sme_page_pa(sd->save_area));
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 6a7686bf6900..447e25c9101a 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -684,6 +684,6 @@ void sev_es_unmap_ghcb(struct vcpu_svm *svm);
 /* vmenter.S */
 
 void __svm_sev_es_vcpu_run(unsigned long vmcb_pa);
-void __svm_vcpu_run(unsigned long vmcb_pa, unsigned long *regs);
+void __svm_vcpu_run(unsigned long vmcb_pa, struct vcpu_svm *svm);
 
 #endif
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index 723f8534986c..f0ff41103e4c 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -4,27 +4,28 @@
 #include <asm/bitsperlong.h>
 #include <asm/kvm_vcpu_regs.h>
 #include <asm/nospec-branch.h>
+#include "kvm-asm-offsets.h"
 
 #define WORD_SIZE (BITS_PER_LONG / 8)
 
 /* Intentionally omit RAX as it's context switched by hardware */
-#define VCPU_RCX	__VCPU_REGS_RCX * WORD_SIZE
-#define VCPU_RDX	__VCPU_REGS_RDX * WORD_SIZE
-#define VCPU_RBX	__VCPU_REGS_RBX * WORD_SIZE
+#define VCPU_RCX	(SVM_vcpu_arch_regs + __VCPU_REGS_RCX * WORD_SIZE)
+#define VCPU_RDX	(SVM_vcpu_arch_regs + __VCPU_REGS_RDX * WORD_SIZE)
+#define VCPU_RBX	(SVM_vcpu_arch_regs + __VCPU_REGS_RBX * WORD_SIZE)
 /* Intentionally omit RSP as it's context switched by hardware */
-#define VCPU_RBP	__VCPU_REGS_RBP * WORD_SIZE
-#define VCPU_RSI	__VCPU_REGS_RSI * WORD_SIZE
-#define VCPU_RDI	__VCPU_REGS_RDI * WORD_SIZE
+#define VCPU_RBP	(SVM_vcpu_arch_regs + __VCPU_REGS_RBP * WORD_SIZE)
+#define VCPU_RSI	(SVM_vcpu_arch_regs + __VCPU_REGS_RSI * WORD_SIZE)
+#define VCPU_RDI	(SVM_vcpu_arch_regs + __VCPU_REGS_RDI * WORD_SIZE)
 
 #ifdef CONFIG_X86_64
-#define VCPU_R8		__VCPU_REGS_R8  * WORD_SIZE
-#define VCPU_R9		__VCPU_REGS_R9  * WORD_SIZE
-#define VCPU_R10	__VCPU_REGS_R10 * WORD_SIZE
-#define VCPU_R11	__VCPU_REGS_R11 * WORD_SIZE
-#define VCPU_R12	__VCPU_REGS_R12 * WORD_SIZE
-#define VCPU_R13	__VCPU_REGS_R13 * WORD_SIZE
-#define VCPU_R14	__VCPU_REGS_R14 * WORD_SIZE
-#define VCPU_R15	__VCPU_REGS_R15 * WORD_SIZE
+#define VCPU_R8		(SVM_vcpu_arch_regs + __VCPU_REGS_R8  * WORD_SIZE)
+#define VCPU_R9		(SVM_vcpu_arch_regs + __VCPU_REGS_R9  * WORD_SIZE)
+#define VCPU_R10	(SVM_vcpu_arch_regs + __VCPU_REGS_R10 * WORD_SIZE)
+#define VCPU_R11	(SVM_vcpu_arch_regs + __VCPU_REGS_R11 * WORD_SIZE)
+#define VCPU_R12	(SVM_vcpu_arch_regs + __VCPU_REGS_R12 * WORD_SIZE)
+#define VCPU_R13	(SVM_vcpu_arch_regs + __VCPU_REGS_R13 * WORD_SIZE)
+#define VCPU_R14	(SVM_vcpu_arch_regs + __VCPU_REGS_R14 * WORD_SIZE)
+#define VCPU_R15	(SVM_vcpu_arch_regs + __VCPU_REGS_R15 * WORD_SIZE)
 #endif
 
 .section .noinstr.text, "ax"
@@ -32,7 +33,7 @@
 /**
  * __svm_vcpu_run - Run a vCPU via a transition to SVM guest mode
  * @vmcb_pa:	unsigned long
- * @regs:	unsigned long * (to guest registers)
+ * @svm:	struct vcpu_svm *
  */
 SYM_FUNC_START(__svm_vcpu_run)
 	push %_ASM_BP
@@ -47,13 +48,13 @@ SYM_FUNC_START(__svm_vcpu_run)
 #endif
 	push %_ASM_BX
 
-	/* Save @regs. */
+	/* Save @svm. */
 	push %_ASM_ARG2
 
 	/* Save @vmcb. */
 	push %_ASM_ARG1
 
-	/* Move @regs to RAX. */
+	/* Move @svm to RAX. */
 	mov %_ASM_ARG2, %_ASM_AX
 
 	/* Load guest registers. */
@@ -89,7 +90,7 @@ SYM_FUNC_START(__svm_vcpu_run)
 	FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
 #endif
 
-	/* "POP" @regs to RAX. */
+	/* "POP" @svm to RAX. */
 	pop %_ASM_AX
 
 	/* Save all guest registers.  */
-- 
2.31.1

Re: [PATCH 02/11] KVM: SVM: replace regs argument of __svm_vcpu_run with vcpu_svm

[Sean Christopherson]

Nit, () on function names.  Maybe I should offer to buy you a beer every time you
remember to add parantheses :-)

On Wed, Nov 09, 2022, Paolo Bonzini wrote:
> Since registers are reachable through vcpu_svm, and we will
> need to access more fields of that struct, pass it instead
> of the regs[] array.
> 
> No functional change intended.
> 
> Cc: stable@vger.kernel.org
> Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@google.com>

[PATCH 03/11] KVM: SVM: adjust register allocation for __svm_vcpu_run

[Paolo Bonzini]

In preparation for moving vmload/vmsave to __svm_vcpu_run,
keep the pointer to the struct vcpu_svm in %rdi.  This way
it is possible to load svm->vmcb01.pa in %rax without
clobbering the pointer to svm itself.

No functional change intended.

Cc: stable@vger.kernel.org
Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/svm/vmenter.S | 38 +++++++++++++++++++-------------------
 1 file changed, 19 insertions(+), 19 deletions(-)

diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index f0ff41103e4c..531510ab6072 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -54,29 +54,29 @@ SYM_FUNC_START(__svm_vcpu_run)
 	/* Save @vmcb. */
 	push %_ASM_ARG1
 
-	/* Move @svm to RAX. */
-	mov %_ASM_ARG2, %_ASM_AX
+	/* Move @svm to RDI. */
+	mov %_ASM_ARG2, %_ASM_DI
+
+	/* "POP" @vmcb to RAX. */
+	pop %_ASM_AX
 
 	/* Load guest registers. */
-	mov VCPU_RCX(%_ASM_AX), %_ASM_CX
-	mov VCPU_RDX(%_ASM_AX), %_ASM_DX
-	mov VCPU_RBX(%_ASM_AX), %_ASM_BX
-	mov VCPU_RBP(%_ASM_AX), %_ASM_BP
-	mov VCPU_RSI(%_ASM_AX), %_ASM_SI
-	mov VCPU_RDI(%_ASM_AX), %_ASM_DI
+	mov VCPU_RCX(%_ASM_DI), %_ASM_CX
+	mov VCPU_RDX(%_ASM_DI), %_ASM_DX
+	mov VCPU_RBX(%_ASM_DI), %_ASM_BX
+	mov VCPU_RBP(%_ASM_DI), %_ASM_BP
+	mov VCPU_RSI(%_ASM_DI), %_ASM_SI
 #ifdef CONFIG_X86_64
-	mov VCPU_R8 (%_ASM_AX),  %r8
-	mov VCPU_R9 (%_ASM_AX),  %r9
-	mov VCPU_R10(%_ASM_AX), %r10
-	mov VCPU_R11(%_ASM_AX), %r11
-	mov VCPU_R12(%_ASM_AX), %r12
-	mov VCPU_R13(%_ASM_AX), %r13
-	mov VCPU_R14(%_ASM_AX), %r14
-	mov VCPU_R15(%_ASM_AX), %r15
+	mov VCPU_R8 (%_ASM_DI),  %r8
+	mov VCPU_R9 (%_ASM_DI),  %r9
+	mov VCPU_R10(%_ASM_DI), %r10
+	mov VCPU_R11(%_ASM_DI), %r11
+	mov VCPU_R12(%_ASM_DI), %r12
+	mov VCPU_R13(%_ASM_DI), %r13
+	mov VCPU_R14(%_ASM_DI), %r14
+	mov VCPU_R15(%_ASM_DI), %r15
 #endif
-
-	/* "POP" @vmcb to RAX. */
-	pop %_ASM_AX
+	mov VCPU_RDI(%_ASM_DI), %_ASM_DI
 
 	/* Enter guest mode */
 	sti
-- 
2.31.1

Re: [PATCH 03/11] KVM: SVM: adjust register allocation for __svm_vcpu_run

[Sean Christopherson]

On Wed, Nov 09, 2022, Paolo Bonzini wrote:
> In preparation for moving vmload/vmsave to __svm_vcpu_run,

__svm_vcpu_run()

> keep the pointer to the struct vcpu_svm in %rdi.  This way
> it is possible to load svm->vmcb01.pa in %rax without
> clobbering the pointer to svm itself.

If you feel like doing fixup before pushing, add a note to call out that avoiding
RAX will also be "necessary" to play nice with loading/storing MSR_SPEC_CTRL?
When fiddling with this code, I found the RDMSR/WRMSR clobbers to be far more
problematic than the VMCB pointers.

> No functional change intended.
> 
> Cc: stable@vger.kernel.org
> Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Reviewed-by: Sean Christopherson <seanjc@google.com>

Re: [PATCH 03/11] KVM: SVM: adjust register allocation for __svm_vcpu_run

[Paolo Bonzini]

On 11/9/22 16:20, Sean Christopherson wrote:
>> keep the pointer to the struct vcpu_svm in %rdi.  This way
>> it is possible to load svm->vmcb01.pa in %rax without
>> clobbering the pointer to svm itself.
>
> If you feel like doing fixup before pushing, add a note to call out that avoiding
> RAX will also be "necessary" to play nice with loading/storing MSR_SPEC_CTRL?
> When fiddling with this code, I found the RDMSR/WRMSR clobbers to be far more
> problematic than the VMCB pointers.

I tried to avoid the "in the future" phrasing which some people dislike. 
  I'll rephrase anyway.  Even without taking 
RDMSR/WRMSR/VMLOAD/VMRUN/VMSAVE into account, avoiding the potential 
clash with 32-bit register arguments is a decent reason for the patch 
anyway.

Paolo

[PATCH 04/11] KVM: SVM: retrieve VMCB from assembly

[Paolo Bonzini]

Continue moving all accesses to struct vcpu_svm directly in vmenter.S.
This limits the confusion due to different registers used for
argument passing in 32- and 64-bit ABIs.

It is not strictly necessary for __svm_sev_es_vcpu_run, but staying
consistent is a good idea since it makes __svm_sev_es_vcpu_run a
stripped version of _svm_vcpu_run.

No functional change intended.

Cc: stable@vger.kernel.org
Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/kvm-asm-offsets.c |  2 ++
 arch/x86/kvm/svm/svm.c         |  5 ++---
 arch/x86/kvm/svm/svm.h         |  4 ++--
 arch/x86/kvm/svm/vmenter.S     | 20 ++++++++++----------
 4 files changed, 16 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kvm/kvm-asm-offsets.c b/arch/x86/kvm/kvm-asm-offsets.c
index 30db96852e2d..f1b694e431ae 100644
--- a/arch/x86/kvm/kvm-asm-offsets.c
+++ b/arch/x86/kvm/kvm-asm-offsets.c
@@ -15,6 +15,8 @@ static void __used common(void)
 	if (IS_ENABLED(CONFIG_KVM_AMD)) {
 		BLANK();
 		OFFSET(SVM_vcpu_arch_regs, vcpu_svm, vcpu.arch.regs);
+		OFFSET(SVM_current_vmcb, vcpu_svm, current_vmcb);
+		OFFSET(KVM_VMCB_pa, kvm_vmcb_info, pa);
 	}
 
 	if (IS_ENABLED(CONFIG_KVM_INTEL)) {
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index b412bc5773c5..0c86c435c51f 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3914,12 +3914,11 @@ static fastpath_t svm_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
 static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
-	unsigned long vmcb_pa = svm->current_vmcb->pa;
 
 	guest_state_enter_irqoff();
 
 	if (sev_es_guest(vcpu->kvm)) {
-		__svm_sev_es_vcpu_run(vmcb_pa);
+		__svm_sev_es_vcpu_run(svm);
 	} else {
 		struct svm_cpu_data *sd = per_cpu(svm_data, vcpu->cpu);
 
@@ -3930,7 +3929,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
 		 * vmcb02 when switching vmcbs for nested virtualization.
 		 */
 		vmload(svm->vmcb01.pa);
-		__svm_vcpu_run(vmcb_pa, svm);
+		__svm_vcpu_run(svm);
 		vmsave(svm->vmcb01.pa);
 
 		vmload(__sme_page_pa(sd->save_area));
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 447e25c9101a..7ff1879e73c5 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -683,7 +683,7 @@ void sev_es_unmap_ghcb(struct vcpu_svm *svm);
 
 /* vmenter.S */
 
-void __svm_sev_es_vcpu_run(unsigned long vmcb_pa);
-void __svm_vcpu_run(unsigned long vmcb_pa, struct vcpu_svm *svm);
+void __svm_sev_es_vcpu_run(struct vcpu_svm *svm);
+void __svm_vcpu_run(struct vcpu_svm *svm);
 
 #endif
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index 531510ab6072..d07bac1952c5 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -32,7 +32,6 @@
 
 /**
  * __svm_vcpu_run - Run a vCPU via a transition to SVM guest mode
- * @vmcb_pa:	unsigned long
  * @svm:	struct vcpu_svm *
  */
 SYM_FUNC_START(__svm_vcpu_run)
@@ -49,16 +48,16 @@ SYM_FUNC_START(__svm_vcpu_run)
 	push %_ASM_BX
 
 	/* Save @svm. */
-	push %_ASM_ARG2
-
-	/* Save @vmcb. */
 	push %_ASM_ARG1
 
+.ifnc _ASM_ARG1, _ASM_DI
 	/* Move @svm to RDI. */
-	mov %_ASM_ARG2, %_ASM_DI
+	mov %_ASM_ARG1, %_ASM_DI
+.endif
 
-	/* "POP" @vmcb to RAX. */
-	pop %_ASM_AX
+	/* Get svm->current_vmcb->pa into RAX. */
+	mov SVM_current_vmcb(%_ASM_DI), %_ASM_AX
+	mov KVM_VMCB_pa(%_ASM_AX), %_ASM_AX
 
 	/* Load guest registers. */
 	mov VCPU_RCX(%_ASM_DI), %_ASM_CX
@@ -170,7 +169,7 @@ SYM_FUNC_END(__svm_vcpu_run)
 
 /**
  * __svm_sev_es_vcpu_run - Run a SEV-ES vCPU via a transition to SVM guest mode
- * @vmcb_pa:	unsigned long
+ * @svm:	struct vcpu_svm *
  */
 SYM_FUNC_START(__svm_sev_es_vcpu_run)
 	push %_ASM_BP
@@ -185,8 +184,9 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
 #endif
 	push %_ASM_BX
 
-	/* Move @vmcb to RAX. */
-	mov %_ASM_ARG1, %_ASM_AX
+	/* Get svm->current_vmcb->pa into RAX. */
+	mov SVM_current_vmcb(%_ASM_ARG1), %_ASM_AX
+	mov KVM_VMCB_pa(%_ASM_AX), %_ASM_AX
 
 	/* Enter guest mode */
 	sti
-- 
2.31.1

Re: [PATCH 04/11] KVM: SVM: retrieve VMCB from assembly

[Sean Christopherson]

On Wed, Nov 09, 2022, Paolo Bonzini wrote:
> Continue moving all accesses to struct vcpu_svm directly in vmenter.S.
> This limits the confusion due to different registers used for
> argument passing in 32- and 64-bit ABIs.
> 
> It is not strictly necessary for __svm_sev_es_vcpu_run, but staying

It's not strictly necessary at all ;-)

__svm_sev_es_vcpu_run()

> consistent is a good idea since it makes __svm_sev_es_vcpu_run a

__svm_sev_es_vcpu_run()

> stripped version of _svm_vcpu_run.

Missed an underscore.  And parantheses.

> No functional change intended.
> 
> Cc: stable@vger.kernel.org
> Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@google.com>

[PATCH 08/11] KVM: SVM: move guest vmsave/vmload back to assembly

[Paolo Bonzini]

FILL_RETURN_BUFFER can access percpu data, therefore vmload of the
host save area must be executed first.  First of all, move the VMCB
vmsave/vmload to assembly, essentially undoing commit fb0c4a4fee5a ("KVM:
SVM: move VMLOAD/VMSAVE to C code", 2021-03-15).  The reason for that
commit was that it made it simpler to use a different VMCB for
VMLOAD/VMSAVE versus VMRUN; but that is not a big hassle anymore thanks
to the kvm-asm-offsets machinery.

The idea on how to number the exception tables is stolen from
a prototype patch by Peter Zijlstra.

Cc: stable@vger.kernel.org
Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
Link: <https://lore.kernel.org/all/f571e404-e625-bae1-10e9-449b2eb4cbd8@citrix.com/>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/kvm-asm-offsets.c |  1 +
 arch/x86/kvm/svm/svm.c         |  9 -------
 arch/x86/kvm/svm/vmenter.S     | 49 ++++++++++++++++++++++++++--------
 3 files changed, 39 insertions(+), 20 deletions(-)

diff --git a/arch/x86/kvm/kvm-asm-offsets.c b/arch/x86/kvm/kvm-asm-offsets.c
index f1b694e431ae..f83e88b85bf2 100644
--- a/arch/x86/kvm/kvm-asm-offsets.c
+++ b/arch/x86/kvm/kvm-asm-offsets.c
@@ -16,6 +16,7 @@ static void __used common(void)
 		BLANK();
 		OFFSET(SVM_vcpu_arch_regs, vcpu_svm, vcpu.arch.regs);
 		OFFSET(SVM_current_vmcb, vcpu_svm, current_vmcb);
+		OFFSET(SVM_vmcb01, vcpu_svm, vmcb01);
 		OFFSET(KVM_VMCB_pa, kvm_vmcb_info, pa);
 	}
 
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 48274c93d78b..4e3a47eb5002 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3910,16 +3910,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
 	} else {
 		struct svm_cpu_data *sd = per_cpu_ptr(&svm_data, vcpu->cpu);
 
-		/*
-		 * Use a single vmcb (vmcb01 because it's always valid) for
-		 * context switching guest state via VMLOAD/VMSAVE, that way
-		 * the state doesn't need to be copied between vmcb01 and
-		 * vmcb02 when switching vmcbs for nested virtualization.
-		 */
-		vmload(svm->vmcb01.pa);
 		__svm_vcpu_run(svm);
-		vmsave(svm->vmcb01.pa);
-
 		vmload(__sme_page_pa(sd->save_area));
 	}
 
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index d07bac1952c5..5bc2ed7d79c0 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -28,6 +28,8 @@
 #define VCPU_R15	(SVM_vcpu_arch_regs + __VCPU_REGS_R15 * WORD_SIZE)
 #endif
 
+#define SVM_vmcb01_pa	(SVM_vmcb01 + KVM_VMCB_pa)
+
 .section .noinstr.text, "ax"
 
 /**
@@ -55,6 +57,16 @@ SYM_FUNC_START(__svm_vcpu_run)
 	mov %_ASM_ARG1, %_ASM_DI
 .endif
 
+	/*
+	 * Use a single vmcb (vmcb01 because it's always valid) for
+	 * context switching guest state via VMLOAD/VMSAVE, that way
+	 * the state doesn't need to be copied between vmcb01 and
+	 * vmcb02 when switching vmcbs for nested virtualization.
+	 */
+	mov SVM_vmcb01_pa(%_ASM_DI), %_ASM_AX
+1:	vmload %_ASM_AX
+2:
+
 	/* Get svm->current_vmcb->pa into RAX. */
 	mov SVM_current_vmcb(%_ASM_DI), %_ASM_AX
 	mov KVM_VMCB_pa(%_ASM_AX), %_ASM_AX
@@ -80,16 +92,11 @@ SYM_FUNC_START(__svm_vcpu_run)
 	/* Enter guest mode */
 	sti
 
-1:	vmrun %_ASM_AX
-
-2:	cli
-
-#ifdef CONFIG_RETPOLINE
-	/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
-	FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
-#endif
+3:	vmrun %_ASM_AX
+4:
+	cli
 
-	/* "POP" @svm to RAX. */
+	/* Pop @svm to RAX while it's the only available register. */
 	pop %_ASM_AX
 
 	/* Save all guest registers.  */
@@ -110,6 +117,18 @@ SYM_FUNC_START(__svm_vcpu_run)
 	mov %r15, VCPU_R15(%_ASM_AX)
 #endif
 
+	/* @svm can stay in RDI from now on.  */
+	mov %_ASM_AX, %_ASM_DI
+
+	mov SVM_vmcb01_pa(%_ASM_DI), %_ASM_AX
+5:	vmsave %_ASM_AX
+6:
+
+#ifdef CONFIG_RETPOLINE
+	/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
+	FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
+#endif
+
 	/*
 	 * Mitigate RETBleed for AMD/Hygon Zen uarch. RET should be
 	 * untrained as soon as we exit the VM and are back to the
@@ -159,11 +178,19 @@ SYM_FUNC_START(__svm_vcpu_run)
 	pop %_ASM_BP
 	RET
 
-3:	cmpb $0, kvm_rebooting
+10:	cmpb $0, kvm_rebooting
 	jne 2b
 	ud2
+30:	cmpb $0, kvm_rebooting
+	jne 4b
+	ud2
+50:	cmpb $0, kvm_rebooting
+	jne 6b
+	ud2
 
-	_ASM_EXTABLE(1b, 3b)
+	_ASM_EXTABLE(1b, 10b)
+	_ASM_EXTABLE(3b, 30b)
+	_ASM_EXTABLE(5b, 50b)
 
 SYM_FUNC_END(__svm_vcpu_run)
 
-- 
2.31.1

Re: [PATCH 08/11] KVM: SVM: move guest vmsave/vmload back to assembly

[Sean Christopherson]

On Wed, Nov 09, 2022, Paolo Bonzini wrote:
> FILL_RETURN_BUFFER can access percpu data, therefore vmload of the
> host save area must be executed first.  First of all, move the VMCB
> vmsave/vmload to assembly, essentially undoing commit fb0c4a4fee5a ("KVM:

Nit, similar to adding parantheses to function names, I prefer capitalizing instruction
mnemonics, i.e. VMSAVE and VMLOAD, to make it obvious that you're referring to a
specific instruction as opposed to a theme/flow.

> SVM: move VMLOAD/VMSAVE to C code", 2021-03-15).  The reason for that
> commit was that it made it simpler to use a different VMCB for
> VMLOAD/VMSAVE versus VMRUN; but that is not a big hassle anymore thanks
> to the kvm-asm-offsets machinery.
> 
> The idea on how to number the exception tables is stolen from
> a prototype patch by Peter Zijlstra.
> 
> Cc: stable@vger.kernel.org
> Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
> Link: <https://lore.kernel.org/all/f571e404-e625-bae1-10e9-449b2eb4cbd8@citrix.com/>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@google.com>

[PATCH 09/11] KVM: SVM: restore host save area from assembly

[Paolo Bonzini]

Allow access to the percpu area via the GS segment base, which is
needed in order to access the saved host spec_ctrl value.  In linux-next
FILL_RETURN_BUFFER also needs to access percpu data.

For simplicity, the physical address of the save area is added to struct
svm_cpu_data.

Cc: stable@vger.kernel.org
Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
Reported-by: Nathan Chancellor <nathan@kernel.org>
Analyzed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/kvm-asm-offsets.c |  1 +
 arch/x86/kvm/svm/svm.c         | 14 ++++++--------
 arch/x86/kvm/svm/svm.h         |  2 ++
 arch/x86/kvm/svm/svm_ops.h     |  5 -----
 arch/x86/kvm/svm/vmenter.S     | 17 +++++++++++++++++
 5 files changed, 26 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/kvm-asm-offsets.c b/arch/x86/kvm/kvm-asm-offsets.c
index f83e88b85bf2..1b805cd24d66 100644
--- a/arch/x86/kvm/kvm-asm-offsets.c
+++ b/arch/x86/kvm/kvm-asm-offsets.c
@@ -18,6 +18,7 @@ static void __used common(void)
 		OFFSET(SVM_current_vmcb, vcpu_svm, current_vmcb);
 		OFFSET(SVM_vmcb01, vcpu_svm, vmcb01);
 		OFFSET(KVM_VMCB_pa, kvm_vmcb_info, pa);
+		OFFSET(SD_save_area_pa, svm_cpu_data, save_area_pa);
 	}
 
 	if (IS_ENABLED(CONFIG_KVM_INTEL)) {
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 4e3a47eb5002..469c1b5617af 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -592,7 +592,7 @@ static int svm_hardware_enable(void)
 
 	wrmsrl(MSR_EFER, efer | EFER_SVME);
 
-	wrmsrl(MSR_VM_HSAVE_PA, __sme_page_pa(sd->save_area));
+	wrmsrl(MSR_VM_HSAVE_PA, sd->save_area_pa);
 
 	if (static_cpu_has(X86_FEATURE_TSCRATEMSR)) {
 		/*
@@ -648,6 +648,7 @@ static void svm_cpu_uninit(int cpu)
 
 	kfree(sd->sev_vmcbs);
 	__free_page(sd->save_area);
+	sd->save_area_pa = 0;
 	sd->save_area = NULL;
 }
 
@@ -665,6 +666,7 @@ static int svm_cpu_init(int cpu)
 	if (ret)
 		goto free_save_area;
 
+	sd->save_area_pa = __sme_page_pa(sd->save_area);
 	return 0;
 
 free_save_area:
@@ -1450,7 +1452,7 @@ static void svm_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
 	 * Save additional host state that will be restored on VMEXIT (sev-es)
 	 * or subsequent vmload of host save area.
 	 */
-	vmsave(__sme_page_pa(sd->save_area));
+	vmsave(sd->save_area_pa);
 	if (sev_es_guest(vcpu->kvm)) {
 		struct sev_es_save_area *hostsa;
 		hostsa = (struct sev_es_save_area *)(page_address(sd->save_area) + 0x400);
@@ -3905,14 +3907,10 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
 
 	guest_state_enter_irqoff();
 
-	if (sev_es_guest(vcpu->kvm)) {
+	if (sev_es_guest(vcpu->kvm))
 		__svm_sev_es_vcpu_run(svm);
-	} else {
-		struct svm_cpu_data *sd = per_cpu_ptr(&svm_data, vcpu->cpu);
-
+	else
 		__svm_vcpu_run(svm);
-		vmload(__sme_page_pa(sd->save_area));
-	}
 
 	guest_state_exit_irqoff();
 }
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 2af6a71126c1..83955a4e520e 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -287,6 +287,8 @@ struct svm_cpu_data {
 	struct kvm_ldttss_desc *tss_desc;
 
 	struct page *save_area;
+	unsigned long save_area_pa;
+
 	struct vmcb *current_vmcb;
 
 	/* index = sev_asid, value = vmcb pointer */
diff --git a/arch/x86/kvm/svm/svm_ops.h b/arch/x86/kvm/svm/svm_ops.h
index 9430d6437c9f..36c8af87a707 100644
--- a/arch/x86/kvm/svm/svm_ops.h
+++ b/arch/x86/kvm/svm/svm_ops.h
@@ -61,9 +61,4 @@ static __always_inline void vmsave(unsigned long pa)
 	svm_asm1(vmsave, "a" (pa), "memory");
 }
 
-static __always_inline void vmload(unsigned long pa)
-{
-	svm_asm1(vmload, "a" (pa), "memory");
-}
-
 #endif /* __KVM_X86_SVM_OPS_H */
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index 5bc2ed7d79c0..57440acfc73e 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -49,6 +49,14 @@ SYM_FUNC_START(__svm_vcpu_run)
 #endif
 	push %_ASM_BX
 
+	/*
+	 * Save variables needed after vmexit on the stack, in inverse
+	 * order compared to when they are needed.
+	 */
+
+	/* Needed to restore access to percpu variables.  */
+	__ASM_SIZE(push) PER_CPU_VAR(svm_data + SD_save_area_pa)
+
 	/* Save @svm. */
 	push %_ASM_ARG1
 
@@ -124,6 +132,11 @@ SYM_FUNC_START(__svm_vcpu_run)
 5:	vmsave %_ASM_AX
 6:
 
+	/* Restores GSBASE among other things, allowing access to percpu data.  */
+	pop %_ASM_AX
+7:	vmload %_ASM_AX
+8:
+
 #ifdef CONFIG_RETPOLINE
 	/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
 	FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
@@ -187,10 +200,14 @@ SYM_FUNC_START(__svm_vcpu_run)
 50:	cmpb $0, kvm_rebooting
 	jne 6b
 	ud2
+70:	cmpb $0, kvm_rebooting
+	jne 8b
+	ud2
 
 	_ASM_EXTABLE(1b, 10b)
 	_ASM_EXTABLE(3b, 30b)
 	_ASM_EXTABLE(5b, 50b)
+	_ASM_EXTABLE(7b, 70b)
 
 SYM_FUNC_END(__svm_vcpu_run)
 
-- 
2.31.1

Re: [PATCH 09/11] KVM: SVM: restore host save area from assembly

[Sean Christopherson]

On Wed, Nov 09, 2022, Paolo Bonzini wrote:
> Allow access to the percpu area via the GS segment base, which is
> needed in order to access the saved host spec_ctrl value.  In linux-next
> FILL_RETURN_BUFFER also needs to access percpu data.
> 
> For simplicity, the physical address of the save area is added to struct
> svm_cpu_data.
> 
> Cc: stable@vger.kernel.org
> Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
> Reported-by: Nathan Chancellor <nathan@kernel.org>
> Analyzed-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Tested-by: Nathan Chancellor <nathan@kernel.org>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@google.com>

> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 2af6a71126c1..83955a4e520e 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -287,6 +287,8 @@ struct svm_cpu_data {
>  	struct kvm_ldttss_desc *tss_desc;
>  
>  	struct page *save_area;
> +	unsigned long save_area_pa;

I really dislike storing both the page and the address, but that's more about
storing the "struct page" instead of the virtual address, and that can be cleaned
up in a follow-up series.

Specifically, the ugly pointer arithmetic in svm_prepare_switch_to_guest() can
be avoided by updating "struct vmcb" to capture SEV-ES+, and by tracking the save
area as a VMCB (which it is).

E.g. as a very partial patch

diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index 0361626841bc..64ba98d32689 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -513,7 +513,10 @@ static inline void __unused_size_checks(void)
 
 struct vmcb {
        struct vmcb_control_area control;
-       struct vmcb_save_area save;
+       union {
+               struct sev_es_save_area sev_es_save;
+               struct vmcb_save_area save;
+       }
 } __packed;
 
 #define SVM_CPUID_FUNC 0x8000000a
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 9f88c8e6766e..b23b7633033b 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1462,12 +1462,8 @@ static void svm_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
         * or subsequent vmload of host save area.
         */
        vmsave(sd->save_area_pa);
-       if (sev_es_guest(vcpu->kvm)) {
-               struct sev_es_save_area *hostsa;
-               hostsa = (struct sev_es_save_area *)(page_address(sd->save_area) + 0x400);
-
-               sev_es_prepare_switch_to_guest(hostsa);
-       }
+       if (sev_es_guest(vcpu->kvm))
+               sev_es_prepare_switch_to_guest(sd->save_area->sev_es_save);
 
        if (tsc_scaling)
                __svm_write_tsc_multiplier(vcpu->arch.tsc_scaling_ratio);
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 199a2ecef1ce..802ed393d860 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -286,7 +286,7 @@ struct svm_cpu_data {
        u32 min_asid;
        struct kvm_ldttss_desc *tss_desc;
 
-       struct page *save_area;
+       struct vmcb *save_area;
        unsigned long save_area_pa;
 
        struct vmcb *current_vmcb;

[PATCH 10/11] KVM: SVM: move MSR_IA32_SPEC_CTRL save/restore to assembly

[Paolo Bonzini]

Restoration of the host IA32_SPEC_CTRL value is probably too late
with respect to the return thunk training sequence.

With respect to the user/kernel boundary, AMD says, "If software chooses
to toggle STIBP (e.g., set STIBP on kernel entry, and clear it on kernel
exit), software should set STIBP to 1 before executing the return thunk
training sequence." I assume the same requirements apply to the guest/host
boundary. The return thunk training sequence is in vmenter.S, quite close
to the VM-exit. On hosts without V_SPEC_CTRL, however, the host's
IA32_SPEC_CTRL value is not restored until much later.

To avoid this, move the restoration of host SPEC_CTRL to assembly and,
for consistency, move the restoration of the guest SPEC_CTRL as well.
This is not particularly difficult, apart from some care to cover both
32- and 64-bit, and to share code between SEV-ES and normal vmentry.

Cc: stable@vger.kernel.org
Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
Suggested-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kernel/cpu/bugs.c     |  13 +---
 arch/x86/kvm/kvm-asm-offsets.c |   1 +
 arch/x86/kvm/svm/svm.c         |  37 ++++------
 arch/x86/kvm/svm/svm.h         |   4 +-
 arch/x86/kvm/svm/vmenter.S     | 119 ++++++++++++++++++++++++++++++++-
 5 files changed, 136 insertions(+), 38 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index da7c361f47e0..6ec0b7ce7453 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -196,22 +196,15 @@ void __init check_bugs(void)
 }
 
 /*
- * NOTE: This function is *only* called for SVM.  VMX spec_ctrl handling is
- * done in vmenter.S.
+ * NOTE: This function is *only* called for SVM, since Intel uses
+ * MSR_IA32_SPEC_CTRL for SSBD.
  */
 void
 x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest)
 {
-	u64 msrval, guestval = guest_spec_ctrl, hostval = spec_ctrl_current();
+	u64 guestval, hostval;
 	struct thread_info *ti = current_thread_info();
 
-	if (static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL)) {
-		if (hostval != guestval) {
-			msrval = setguest ? guestval : hostval;
-			wrmsrl(MSR_IA32_SPEC_CTRL, msrval);
-		}
-	}
-
 	/*
 	 * If SSBD is not handled in MSR_SPEC_CTRL on AMD, update
 	 * MSR_AMD64_L2_CFG or MSR_VIRT_SPEC_CTRL if supported.
diff --git a/arch/x86/kvm/kvm-asm-offsets.c b/arch/x86/kvm/kvm-asm-offsets.c
index 1b805cd24d66..24a710d37323 100644
--- a/arch/x86/kvm/kvm-asm-offsets.c
+++ b/arch/x86/kvm/kvm-asm-offsets.c
@@ -16,6 +16,7 @@ static void __used common(void)
 		BLANK();
 		OFFSET(SVM_vcpu_arch_regs, vcpu_svm, vcpu.arch.regs);
 		OFFSET(SVM_current_vmcb, vcpu_svm, current_vmcb);
+		OFFSET(SVM_spec_ctrl, vcpu_svm, spec_ctrl);
 		OFFSET(SVM_vmcb01, vcpu_svm, vmcb01);
 		OFFSET(KVM_VMCB_pa, kvm_vmcb_info, pa);
 		OFFSET(SD_save_area_pa, svm_cpu_data, save_area_pa);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 469c1b5617af..cf1aed25f4ab 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -720,6 +720,15 @@ static bool msr_write_intercepted(struct kvm_vcpu *vcpu, u32 msr)
 	u32 offset;
 	u32 *msrpm;
 
+	/*
+	 * For non-nested case:
+	 * If the L01 MSR bitmap does not intercept the MSR, then we need to
+	 * save it.
+	 *
+	 * For nested case:
+	 * If the L02 MSR bitmap does not intercept the MSR, then we need to
+	 * save it.
+	 */
 	msrpm = is_guest_mode(vcpu) ? to_svm(vcpu)->nested.msrpm:
 				      to_svm(vcpu)->msrpm;
 
@@ -3901,16 +3910,16 @@ static fastpath_t svm_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
 	return EXIT_FASTPATH_NONE;
 }
 
-static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
+static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu, bool spec_ctrl_intercepted)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
 	guest_state_enter_irqoff();
 
 	if (sev_es_guest(vcpu->kvm))
-		__svm_sev_es_vcpu_run(svm);
+		__svm_sev_es_vcpu_run(svm, spec_ctrl_intercepted);
 	else
-		__svm_vcpu_run(svm);
+		__svm_vcpu_run(svm, spec_ctrl_intercepted);
 
 	guest_state_exit_irqoff();
 }
@@ -3918,6 +3927,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
 static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
+	bool spec_ctrl_intercepted = msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL);
 
 	trace_kvm_entry(vcpu);
 
@@ -3976,26 +3986,7 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
 	if (!static_cpu_has(X86_FEATURE_V_SPEC_CTRL))
 		x86_spec_ctrl_set_guest(svm->spec_ctrl, svm->virt_spec_ctrl);
 
-	svm_vcpu_enter_exit(vcpu);
-
-	/*
-	 * We do not use IBRS in the kernel. If this vCPU has used the
-	 * SPEC_CTRL MSR it may have left it on; save the value and
-	 * turn it off. This is much more efficient than blindly adding
-	 * it to the atomic save/restore list. Especially as the former
-	 * (Saving guest MSRs on vmexit) doesn't even exist in KVM.
-	 *
-	 * For non-nested case:
-	 * If the L01 MSR bitmap does not intercept the MSR, then we need to
-	 * save it.
-	 *
-	 * For nested case:
-	 * If the L02 MSR bitmap does not intercept the MSR, then we need to
-	 * save it.
-	 */
-	if (!static_cpu_has(X86_FEATURE_V_SPEC_CTRL) &&
-	    unlikely(!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL)))
-		svm->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);
+	svm_vcpu_enter_exit(vcpu, spec_ctrl_intercepted);
 
 	if (!sev_es_guest(vcpu->kvm))
 		reload_tss(vcpu);
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 83955a4e520e..199a2ecef1ce 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -682,7 +682,7 @@ void sev_es_unmap_ghcb(struct vcpu_svm *svm);
 
 /* vmenter.S */
 
-void __svm_sev_es_vcpu_run(struct vcpu_svm *svm);
-void __svm_vcpu_run(struct vcpu_svm *svm);
+void __svm_sev_es_vcpu_run(struct vcpu_svm *svm, bool spec_ctrl_intercepted);
+void __svm_vcpu_run(struct vcpu_svm *svm, bool spec_ctrl_intercepted);
 
 #endif
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index 57440acfc73e..34367dc203f2 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -32,9 +32,69 @@
 
 .section .noinstr.text, "ax"
 
+.macro RESTORE_GUEST_SPEC_CTRL
+	/* No need to do anything if SPEC_CTRL is unset or V_SPEC_CTRL is set */
+	ALTERNATIVE_2 "", \
+		"jmp 800f", X86_FEATURE_MSR_SPEC_CTRL, \
+		"", X86_FEATURE_V_SPEC_CTRL
+801:
+.endm
+.macro RESTORE_GUEST_SPEC_CTRL_BODY
+800:
+	/*
+	 * SPEC_CTRL handling: if the guest's SPEC_CTRL value differs from the
+	 * host's, write the MSR.  This is kept out-of-line so that the common
+	 * case does not have to jump.
+	 *
+	 * IMPORTANT: To avoid RSB underflow attacks and any other nastiness,
+	 * there must not be any returns or indirect branches between this code
+	 * and vmentry.
+	 */
+	movl SVM_spec_ctrl(%_ASM_DI), %eax
+	cmp PER_CPU_VAR(x86_spec_ctrl_current), %eax
+	je 801b
+	mov $MSR_IA32_SPEC_CTRL, %ecx
+	xor %edx, %edx
+	wrmsr
+	jmp 801b
+.endm
+
+.macro RESTORE_HOST_SPEC_CTRL
+	/* No need to do anything if SPEC_CTRL is unset or V_SPEC_CTRL is set */
+	ALTERNATIVE_2 "", \
+		"jmp 900f", X86_FEATURE_MSR_SPEC_CTRL, \
+		"", X86_FEATURE_V_SPEC_CTRL
+901:
+.endm
+.macro RESTORE_HOST_SPEC_CTRL_BODY
+900:
+	/* Same for after vmexit.  */
+	mov $MSR_IA32_SPEC_CTRL, %ecx
+
+	/*
+	 * Load the value that the guest had written into MSR_IA32_SPEC_CTRL,
+	 * if it was not intercepted during guest execution.
+	 */
+	cmpb $0, (%_ASM_SP)
+	jnz 998f
+	rdmsr
+	movl %eax, SVM_spec_ctrl(%_ASM_DI)
+998:
+
+	/* Now restore the host value of the MSR if different from the guest's.  */
+	movl PER_CPU_VAR(x86_spec_ctrl_current), %eax
+	cmp SVM_spec_ctrl(%_ASM_DI), %eax
+	je 901b
+	xor %edx, %edx
+	wrmsr
+	jmp 901b
+.endm
+
+
 /**
  * __svm_vcpu_run - Run a vCPU via a transition to SVM guest mode
  * @svm:	struct vcpu_svm *
+ * @spec_ctrl_intercepted: bool
  */
 SYM_FUNC_START(__svm_vcpu_run)
 	push %_ASM_BP
@@ -54,17 +114,26 @@ SYM_FUNC_START(__svm_vcpu_run)
 	 * order compared to when they are needed.
 	 */
 
+	/* Accessed directly from the stack in RESTORE_HOST_SPEC_CTRL.  */
+	push %_ASM_ARG2
+
 	/* Needed to restore access to percpu variables.  */
 	__ASM_SIZE(push) PER_CPU_VAR(svm_data + SD_save_area_pa)
 
-	/* Save @svm. */
+	/* Finally save @svm. */
 	push %_ASM_ARG1
 
 .ifnc _ASM_ARG1, _ASM_DI
-	/* Move @svm to RDI. */
+	/*
+	 * Stash @svm in RDI early. On 32-bit, arguments are in RAX, RCX
+	 * and RDX which are clobbered by RESTORE_GUEST_SPEC_CTRL.
+	 */
 	mov %_ASM_ARG1, %_ASM_DI
 .endif
 
+	/* Clobbers RAX, RCX, RDX.  */
+	RESTORE_GUEST_SPEC_CTRL
+
 	/*
 	 * Use a single vmcb (vmcb01 because it's always valid) for
 	 * context switching guest state via VMLOAD/VMSAVE, that way
@@ -142,6 +211,9 @@ SYM_FUNC_START(__svm_vcpu_run)
 	FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
 #endif
 
+	/* Clobbers RAX, RCX, RDX.  */
+	RESTORE_HOST_SPEC_CTRL
+
 	/*
 	 * Mitigate RETBleed for AMD/Hygon Zen uarch. RET should be
 	 * untrained as soon as we exit the VM and are back to the
@@ -177,6 +249,9 @@ SYM_FUNC_START(__svm_vcpu_run)
 	xor %r15d, %r15d
 #endif
 
+	/* "Pop" @spec_ctrl_intercepted.  */
+	pop %_ASM_BX
+
 	pop %_ASM_BX
 
 #ifdef CONFIG_X86_64
@@ -191,6 +266,9 @@ SYM_FUNC_START(__svm_vcpu_run)
 	pop %_ASM_BP
 	RET
 
+	RESTORE_GUEST_SPEC_CTRL_BODY
+	RESTORE_HOST_SPEC_CTRL_BODY
+
 10:	cmpb $0, kvm_rebooting
 	jne 2b
 	ud2
@@ -214,6 +292,7 @@ SYM_FUNC_END(__svm_vcpu_run)
 /**
  * __svm_sev_es_vcpu_run - Run a SEV-ES vCPU via a transition to SVM guest mode
  * @svm:	struct vcpu_svm *
+ * @spec_ctrl_intercepted: bool
  */
 SYM_FUNC_START(__svm_sev_es_vcpu_run)
 	push %_ASM_BP
@@ -228,8 +307,30 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
 #endif
 	push %_ASM_BX
 
+	/*
+	 * Save variables needed after vmexit on the stack, in inverse
+	 * order compared to when they are needed.
+	 */
+
+	/* Accessed directly from the stack in RESTORE_HOST_SPEC_CTRL.  */
+	push %_ASM_ARG2
+
+	/* Save @svm. */
+	push %_ASM_ARG1
+
+.ifnc _ASM_ARG1, _ASM_DI
+	/*
+	 * Stash @svm in RDI early. On 32-bit, arguments are in RAX, RCX
+	 * and RDX which are clobbered by RESTORE_GUEST_SPEC_CTRL.
+	 */
+	mov %_ASM_ARG1, %_ASM_DI
+.endif
+
+	/* Clobbers RAX, RCX, RDX.  */
+	RESTORE_GUEST_SPEC_CTRL
+
 	/* Get svm->current_vmcb->pa into RAX. */
-	mov SVM_current_vmcb(%_ASM_ARG1), %_ASM_AX
+	mov SVM_current_vmcb(%_ASM_DI), %_ASM_AX
 	mov KVM_VMCB_pa(%_ASM_AX), %_ASM_AX
 
 	/* Enter guest mode */
@@ -239,11 +340,17 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
 
 2:	cli
 
+	/* Pop @svm to RDI, guest registers have been saved already. */
+	pop %_ASM_DI
+
 #ifdef CONFIG_RETPOLINE
 	/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
 	FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
 #endif
 
+	/* Clobbers RAX, RCX, RDX.  */
+	RESTORE_HOST_SPEC_CTRL
+
 	/*
 	 * Mitigate RETBleed for AMD/Hygon Zen uarch. RET should be
 	 * untrained as soon as we exit the VM and are back to the
@@ -253,6 +360,9 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
 	 */
 	UNTRAIN_RET
 
+	/* "Pop" @spec_ctrl_intercepted.  */
+	pop %_ASM_BX
+
 	pop %_ASM_BX
 
 #ifdef CONFIG_X86_64
@@ -267,6 +377,9 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
 	pop %_ASM_BP
 	RET
 
+	RESTORE_GUEST_SPEC_CTRL_BODY
+	RESTORE_HOST_SPEC_CTRL_BODY
+
 3:	cmpb $0, kvm_rebooting
 	jne 2b
 	ud2
-- 
2.31.1

Re: [PATCH 10/11] KVM: SVM: move MSR_IA32_SPEC_CTRL save/restore to assembly

[Sean Christopherson]

On Wed, Nov 09, 2022, Paolo Bonzini wrote:
> Restoration of the host IA32_SPEC_CTRL value is probably too late
> with respect to the return thunk training sequence.
> 
> With respect to the user/kernel boundary, AMD says, "If software chooses
> to toggle STIBP (e.g., set STIBP on kernel entry, and clear it on kernel
> exit), software should set STIBP to 1 before executing the return thunk
> training sequence." I assume the same requirements apply to the guest/host
> boundary. The return thunk training sequence is in vmenter.S, quite close
> to the VM-exit. On hosts without V_SPEC_CTRL, however, the host's
> IA32_SPEC_CTRL value is not restored until much later.
> 
> To avoid this, move the restoration of host SPEC_CTRL to assembly and,
> for consistency, move the restoration of the guest SPEC_CTRL as well.
> This is not particularly difficult, apart from some care to cover both
> 32- and 64-bit, and to share code between SEV-ES and normal vmentry.
> 
> Cc: stable@vger.kernel.org
> Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
> Suggested-by: Jim Mattson <jmattson@google.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@google.com>

> +.ifnc _ASM_ARG1, _ASM_DI
> +	/*
> +	 * Stash @svm in RDI early. On 32-bit, arguments are in RAX, RCX
> +	 * and RDX which are clobbered by RESTORE_GUEST_SPEC_CTRL.
> +	 */
> +	mov %_ASM_ARG1, %_ASM_DI
> +.endif

Not technically needed since SEV-ES is 64-bit only, but that's a pre-exisiting
mess.  I'll send a follow-up patch to #ifdef out the entire function and drop all
of this internal ifdeffery, and provide a stub in C code stub in C code so that
32-bit can link (and kill the VM if if the stub is reached).