Commit 8ed12ab1 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Ingo Molnar
Browse files

x86/boot/sev: Support memory acceptance in the EFI stub under SVSM 



Commit:

  d54d6102 ("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: fcd042e8 ("x86/sev: Perform PVALIDATE using the SVSM when not at VMPL0")
Tested-by: default avatarTom Lendacky <thomas.lendacky@amd.com>
Co-developed-by: default avatarTom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: default avatarTom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarIngo 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
parent b4432656

arch/x86/boot/compressed/mem.c

+1 −4
Original line number Diff line number Diff line
@@ -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");

arch/x86/boot/compressed/sev.c

+40 −0
Original line number Diff line number Diff line
@@ -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;

}

arch/x86/boot/compressed/sev.h

+2 −0
Original line number Diff line number Diff line
@@ -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