[PATCHv7 14/14] x86/tdx: Add unaccepted memory support

Kirill A. Shutemov
2022-06-14T12:03:12Z

Hookup TDX-specific code to accept memory.

Accepting the memory is the same process as converting memory from
shared to private: kernel notifies VMM with MAP_GPA hypercall and then
accept pages with ACCEPT_PAGE module call.

The implementation in core kernel uses tdx_enc_status_changed(). It
already used for converting memory to shared and back for I/O
transactions.

Boot stub provides own implementation of tdx_accept_memory(). It is
similar in structure to tdx_enc_status_changed(), but only cares about
converting memory to private.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
arch/x86/Kconfig | 1 +
arch/x86/boot/compressed/mem.c | 27 ++++++++++-
arch/x86/boot/compressed/tdx.c | 78 +++++++++++++++++++++++++++++++
arch/x86/coco/tdx/tdx.c | 30 ++++++++----
arch/x86/include/asm/shared/tdx.h | 2 +
arch/x86/mm/unaccepted_memory.c | 9 +++-
6 files changed, 136 insertions(+), 11 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 9783ebc4e021..80683afa5749 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -892,6 +892,7 @@ config INTEL_TDX_GUEST
select ARCH_HAS_CC_PLATFORM
select X86_MEM_ENCRYPT
select X86_MCE
+ select UNACCEPTED_MEMORY
help
Support running as a guest under Intel TDX. Without this support,
the guest kernel can not boot or run under TDX.
diff --git a/arch/x86/boot/compressed/mem.c b/arch/x86/boot/compressed/mem.c
index b45458af00ca..48e36e640da1 100644
--- a/arch/x86/boot/compressed/mem.c
+++ b/arch/x86/boot/compressed/mem.c
@@ -5,6 +5,8 @@
#include "error.h"
#include "find.h"
#include "math.h"
+#include "tdx.h"
+#include <asm/shared/tdx.h>

#define PMD_SHIFT 21
#define PMD_SIZE (_AC(1, UL) << PMD_SHIFT)
@@ -12,10 +14,33 @@

extern struct boot_params *boot_params;

+static bool is_tdx_guest(void)
+{
+ static bool once;
+ static bool is_tdx;
+
+ if (!IS_ENABLED(CONFIG_INTEL_TDX_GUEST))
+ return false;
+
+ if (!once) {
+ u32 eax, sig[3];
+
+ cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax,
+ &sig[0], &sig[2], &sig[1]);
+ is_tdx = !memcmp(TDX_IDENT, sig, sizeof(sig));
+ once = true;
+ }
+
+ return is_tdx;
+}
+
static inline void __accept_memory(phys_addr_t start, phys_addr_t end)
{
/* Platform-specific memory-acceptance call goes here */
- error("Cannot accept memory");
+ if (is_tdx_guest())
+ tdx_accept_memory(start, end);
+ else
+ error("Cannot accept memory: unknown platform\n");
}

/*
diff --git a/arch/x86/boot/compressed/tdx.c b/arch/x86/boot/compressed/tdx.c
index 918a7606f53c..8518a75e5dd5 100644
--- a/arch/x86/boot/compressed/tdx.c
+++ b/arch/x86/boot/compressed/tdx.c
@@ -3,12 +3,15 @@
#include "../cpuflags.h"
#include "../string.h"
#include "../io.h"
+#include "align.h"
#include "error.h"
+#include "pgtable_types.h"

#include <vdso/limits.h>
#include <uapi/asm/vmx.h>

#include <asm/shared/tdx.h>
+#include <asm/page_types.h>

/* Called from __tdx_hypercall() for unrecoverable failure */
void __tdx_hypercall_failed(void)
@@ -75,3 +78,78 @@ void early_tdx_detect(void)
pio_ops.f_outb = tdx_outb;
pio_ops.f_outw = tdx_outw;
}
+
+static unsigned long try_accept_one(phys_addr_t start, unsigned long len,
+ enum pg_level level)
+{
+ unsigned long accept_size = PAGE_SIZE << ((level - 1) * PTE_SHIFT);
+ u64 tdcall_rcx;
+ u8 page_size;
+
+ if (!IS_ALIGNED(start, accept_size))
+ return 0;
+
+ if (len < accept_size)
+ return 0;
+
+ /*
+ * Pass the page physical address to the TDX module to accept the
+ * pending, private page.
+ *
+ * Bits 2:0 of RCX encode page size: 0 - 4K, 1 - 2M, 2 - 1G.
+ */
+ switch (level) {
+ case PG_LEVEL_4K:
+ page_size = 0;
+ break;
+ case PG_LEVEL_2M:
+ page_size = 1;
+ break;
+ case PG_LEVEL_1G:
+ page_size = 2;
+ break;
+ default:
+ return 0;
+ }
+
+ tdcall_rcx = start | page_size;
+ if (__tdx_module_call(TDX_ACCEPT_PAGE, tdcall_rcx, 0, 0, 0, NULL))
+ return 0;
+
+ return accept_size;
+}
+
+void tdx_accept_memory(phys_addr_t start, phys_addr_t end)
+{
+ /*
+ * Notify the VMM about page mapping conversion. More info about ABI
+ * can be found in TDX Guest-Host-Communication Interface (GHCI),
+ * section "TDG.VP.VMCALL<MapGPA>"
+ */
+ if (_tdx_hypercall(TDVMCALL_MAP_GPA, start, end - start, 0, 0))
+ error("Accepting memory failed\n");
+
+ /*
+ * For shared->private conversion, accept the page using
+ * TDX_ACCEPT_PAGE TDX module call.
+ */
+ while (start < end) {
+ unsigned long len = end - start;
+ unsigned long accept_size;
+
+ /*
+ * Try larger accepts first. It gives chance to VMM to keep
+ * 1G/2M Secure EPT entries where possible and speeds up
+ * process by cutting number of hypercalls (if successful).
+ */
+
+ accept_size = try_accept_one(start, len, PG_LEVEL_1G);
+ if (!accept_size)
+ accept_size = try_accept_one(start, len, PG_LEVEL_2M);
+ if (!accept_size)
+ accept_size = try_accept_one(start, len, PG_LEVEL_4K);
+ if (!accept_size)
+ error("Accepting memory failed\n");
+ start += accept_size;
+ }
+}
diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index b10c95307f6e..8240f04d3646 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -664,16 +664,9 @@ static unsigned long try_accept_one(phys_addr_t start, unsigned long len,
return accept_size;
}

-/*
- * Inform the VMM of the guest's intent for this physical page: shared with
- * the VMM or private to the guest. The VMM is expected to change its mapping
- * of the page in response.
- */
-static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
+static bool tdx_enc_status_changed_phys(phys_addr_t start, phys_addr_t end,
+ bool enc)
{
- phys_addr_t start = __pa(vaddr);
- phys_addr_t end = __pa(vaddr + numpages * PAGE_SIZE);
-
if (!enc) {
/* Set the shared (decrypted) bits: */
start |= cc_mkdec(0);
@@ -719,6 +712,25 @@ static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
return true;
}

+void tdx_accept_memory(phys_addr_t start, phys_addr_t end)
+{
+ if (!tdx_enc_status_changed_phys(start, end, true))
+ panic("Accepting memory failed: %#llx-%#llx\n", start, end);
+}
+
+/*
+ * Inform the VMM of the guest's intent for this physical page: shared with
+ * the VMM or private to the guest. The VMM is expected to change its mapping
+ * of the page in response.
+ */
+static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
+{
+ phys_addr_t start = __pa(vaddr);
+ phys_addr_t end = __pa(vaddr + numpages * PAGE_SIZE);
+
+ return tdx_enc_status_changed_phys(start, end, enc);
+}
+
void __init tdx_early_init(void)
{
u64 cc_mask;
diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
index 956ced04c3be..97534c334473 100644
--- a/arch/x86/include/asm/shared/tdx.h
+++ b/arch/x86/include/asm/shared/tdx.h
@@ -81,5 +81,7 @@ struct tdx_module_output {
u64 __tdx_module_call(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
struct tdx_module_output *out);

+void tdx_accept_memory(phys_addr_t start, phys_addr_t end);
+
#endif /* !__ASSEMBLY__ */
#endif /* _ASM_X86_SHARED_TDX_H */
diff --git a/arch/x86/mm/unaccepted_memory.c b/arch/x86/mm/unaccepted_memory.c
index 05e216716690..9ec2304272dc 100644
--- a/arch/x86/mm/unaccepted_memory.c
+++ b/arch/x86/mm/unaccepted_memory.c
@@ -7,6 +7,7 @@

#include <asm/io.h>
#include <asm/setup.h>
+#include <asm/shared/tdx.h>
#include <asm/unaccepted_memory.h>

/* Protects unaccepted memory bitmap */
@@ -62,7 +63,13 @@ void accept_memory(phys_addr_t start, phys_addr_t end)
unsigned long len = range_end - range_start;

/* Platform-specific memory-acceptance call goes here */
- panic("Cannot accept memory: unknown platform\n");
+ if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST)) {
+ tdx_accept_memory(range_start * PMD_SIZE,
+ range_end * PMD_SIZE);
+ } else {
+ panic("Cannot accept memory: unknown platform\n");
+ }
+
bitmap_clear(bitmap, range_start, len);
}
spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
--
2.35.1