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Fix SEV-SNP memory acceptance from the EFI stub for guests

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running at VMPL >0.
 
 Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'x86-urgent-2025-05-04' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 fix from Ingo Molnar:
 "Fix SEV-SNP memory acceptance from the EFI stub for guests
  running at VMPL >0"

* tag 'x86-urgent-2025-05-04' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/boot/sev: Support memory acceptance in the EFI stub under SVSM
This commit is contained in:
Linus Torvalds 2025-05-04 08:12:03 -07:00
commit 3d84c97a8d
3 changed files with 43 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

5
arch/x86/boot/compressed/mem.c
View file

@ -34,14 +34,11 @@ static bool early_is_tdx_guest(void)
void arch_accept_memory(phys_addr_t start, phys_addr_t end)
{
static bool sevsnp;
/* Platform-specific memory-acceptance call goes here */
if (early_is_tdx_guest()) {
if (!tdx_accept_memory(start, end))
panic("TDX: Failed to accept memory\n");
} else if (sevsnp || (sev_get_status() & MSR_AMD64_SEV_SNP_ENABLED)) {
sevsnp = true;
} else if (early_is_sevsnp_guest()) {
snp_accept_memory(start, end);
} else {
error("Cannot accept memory: unknown platform\n");

40
arch/x86/boot/compressed/sev.c
View file

@ -645,3 +645,43 @@ void sev_prep_identity_maps(unsigned long top_level_pgt)
sev_verify_cbit(top_level_pgt);
}
bool early_is_sevsnp_guest(void)
{
static bool sevsnp;
if (sevsnp)
return true;
if (!(sev_get_status() & MSR_AMD64_SEV_SNP_ENABLED))
return false;
sevsnp = true;
if (!snp_vmpl) {
unsigned int eax, ebx, ecx, edx;
/*
* CPUID Fn8000_001F_EAX[28] - SVSM support
*/
eax = 0x8000001f;
ecx = 0;
native_cpuid(&eax, &ebx, &ecx, &edx);
if (eax & BIT(28)) {
struct msr m;
/* Obtain the address of the calling area to use */
boot_rdmsr(MSR_SVSM_CAA, &m);
boot_svsm_caa = (void *)m.q;
boot_svsm_caa_pa = m.q;
/*
* The real VMPL level cannot be discovered, but the
* memory acceptance routines make no use of that so
* any non-zero value suffices here.
*/
snp_vmpl = U8_MAX;
}
}
return true;
}

2
arch/x86/boot/compressed/sev.h
View file

@ -13,12 +13,14 @@
bool sev_snp_enabled(void);
void snp_accept_memory(phys_addr_t start, phys_addr_t end);
u64 sev_get_status(void);
bool early_is_sevsnp_guest(void);
#else
static inline bool sev_snp_enabled(void) { return false; }
static inline void snp_accept_memory(phys_addr_t start, phys_addr_t end) { }
static inline u64 sev_get_status(void) { return 0; }
static inline bool early_is_sevsnp_guest(void) { return false; }
#endif