Commit 3645eb7e authored by Nikunj A Dadhania's avatar Nikunj A Dadhania Committed by Borislav Petkov (AMD)
Browse files

x86/fred: Fix early boot failures on SEV-ES/SNP guests 



FRED-enabled SEV-(ES,SNP) guests fail to boot due to the following issues
in the early boot sequence:

* FRED does not have a #VC exception handler in the dispatch logic

* Early FRED #VC exceptions attempt to use uninitialized per-CPU GHCBs
  instead of boot_ghcb

Add X86_TRAP_VC case to fred_hwexc() with a new exc_vmm_communication()
function that provides the unified entry point FRED requires, dispatching
to existing user/kernel handlers based on privilege level. The function is
already declared via DECLARE_IDTENTRY_VC().

Fix early GHCB access by falling back to boot_ghcb in
__sev_{get,put}_ghcb() when per-CPU GHCBs are not yet initialized.

Fixes: 14619d91 ("x86/fred: FRED entry/exit and dispatch code")
Signed-off-by: default avatarNikunj A Dadhania <nikunj@amd.com>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: default avatarTom Lendacky <thomas.lendacky@amd.com>
Cc: <stable@kernel.org>  # 6.12+
Link: https://patch.msgid.link/20260318075654.1792916-4-nikunj@amd.com
parent 411df123

arch/x86/coco/sev/noinstr.c

+6 −0
Original line number Diff line number Diff line
@@ -121,6 +121,9 @@ noinstr struct ghcb *__sev_get_ghcb(struct ghcb_state *state) 


	WARN_ON(!irqs_disabled());



	if (!sev_cfg.ghcbs_initialized)

		return boot_ghcb;



	data = this_cpu_read(runtime_data);

	ghcb = &data->ghcb_page;
@@ -164,6 +167,9 @@ noinstr void __sev_put_ghcb(struct ghcb_state *state) 


	WARN_ON(!irqs_disabled());



	if (!sev_cfg.ghcbs_initialized)

		return;



	data = this_cpu_read(runtime_data);

	ghcb = &data->ghcb_page;

arch/x86/entry/entry_fred.c

+14 −0
Original line number Diff line number Diff line
@@ -177,6 +177,16 @@ static noinstr void fred_extint(struct pt_regs *regs) 
	}

}



#ifdef CONFIG_AMD_MEM_ENCRYPT

noinstr void exc_vmm_communication(struct pt_regs *regs, unsigned long error_code)

{

	if (user_mode(regs))

		return user_exc_vmm_communication(regs, error_code);

	else

		return kernel_exc_vmm_communication(regs, error_code);

}

#endif



static noinstr void fred_hwexc(struct pt_regs *regs, unsigned long error_code)

{

	/* Optimize for #PF. That's the only exception which matters performance wise */
@@ -207,6 +217,10 @@ static noinstr void fred_hwexc(struct pt_regs *regs, unsigned long error_code) 
#ifdef CONFIG_X86_CET

	case X86_TRAP_CP: return exc_control_protection(regs, error_code);

#endif

#ifdef CONFIG_AMD_MEM_ENCRYPT

	case X86_TRAP_VC: return exc_vmm_communication(regs, error_code);

#endif



	default: return fred_bad_type(regs, error_code);

	}