6.12-stable review patch. If anyone has any objections, please let me know.
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From: Ard Biesheuvel ardb@kernel.org
commit 8ed12ab1319b2d8e4a529504777aacacf71371e4 upstream.
Commit:
d54d610243a4 ("x86/boot/sev: Avoid shared GHCB page for early memory acceptance")
provided a fix for SEV-SNP memory acceptance from the EFI stub when running at VMPL #0. However, that fix was insufficient for SVSM SEV-SNP guests running at VMPL >0, as those rely on a SVSM calling area, which is a shared buffer whose address is programmed into a SEV-SNP MSR, and the SEV init code that sets up this calling area executes much later during the boot.
Given that booting via the EFI stub at VMPL >0 implies that the firmware has configured this calling area already, reuse it for performing memory acceptance in the EFI stub.
Fixes: fcd042e86422 ("x86/sev: Perform PVALIDATE using the SVSM when not at VMPL0") Tested-by: Tom Lendacky thomas.lendacky@amd.com Co-developed-by: Tom Lendacky thomas.lendacky@amd.com Signed-off-by: Tom Lendacky thomas.lendacky@amd.com Signed-off-by: Ard Biesheuvel ardb@kernel.org Signed-off-by: Ingo Molnar mingo@kernel.org Cc: stable@vger.kernel.org Cc: Dionna Amalie Glaze dionnaglaze@google.com Cc: Kevin Loughlin kevinloughlin@google.com Cc: linux-efi@vger.kernel.org Link: https://lore.kernel.org/r/20250428174322.2780170-2-ardb+git@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/boot/compressed/mem.c | 5 +---- arch/x86/boot/compressed/sev.c | 40 ++++++++++++++++++++++++++++++++++++++++ arch/x86/boot/compressed/sev.h | 2 ++ 3 files changed, 43 insertions(+), 4 deletions(-)
--- a/arch/x86/boot/compressed/mem.c +++ b/arch/x86/boot/compressed/mem.c @@ -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"); --- a/arch/x86/boot/compressed/sev.c +++ b/arch/x86/boot/compressed/sev.c @@ -644,3 +644,43 @@ void sev_prep_identity_maps(unsigned lon
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; +} --- a/arch/x86/boot/compressed/sev.h +++ b/arch/x86/boot/compressed/sev.h @@ -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