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: 14619d912b65 ("x86/fred: FRED entry/exit and dispatch code")
Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: <stable@kernel.org>  # 6.12+
Link: https://patch.msgid.link/20260318075654.1792916-4-nikunj@amd.com

diff --git a/arch/x86/coco/sev/noinstr.c b/arch/x86/coco/sev/noinstr.c
index 9d94aca4a698f6dc1d535107abb67ec43a7d263b..5afd663a1c217aca9d15c168f5a049fff55c49ca 100644 (file)
--- a/arch/x86/coco/sev/noinstr.c
+++ b/arch/x86/coco/sev/noinstr.c
@@ -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;
 

diff --git a/arch/x86/entry/entry_fred.c b/arch/x86/entry/entry_fred.c
index 88c757ac8ccd4897709e64f3e487f4e37a8b2933..fbe2d10dd737daef6603873150024407753e2d5b 100644 (file)
--- a/arch/x86/entry/entry_fred.c
+++ b/arch/x86/entry/entry_fred.c
@@ -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);
        }