[PATCH v2 2/2] x86/sev-es: Invalidate the GHCB after completing VMGEXIT

[Tom Lendacky <thomas.lendacky@amd.com>]

Since the VMGEXIT instruction can be issued from userspace, invalidate
the GHCB after performing VMGEXIT processing in the kernel.

Invalidation is only required after userspace is available, so call
vc_ghcb_invalidate() from sev_es_put_ghcb(). Update vc_ghcb_invalidate()
to additionally clear the GHCB exit code, so that a value of 0 is always
present outside VMGEXIT processing in the kernel.

Fixes: 0786138c78e79 ("x86/sev-es: Add a Runtime #VC Exception Handler")
Cc: stable@vger.kernel.org
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 arch/x86/kernel/sev-shared.c | 1 +
 arch/x86/kernel/sev.c        | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 6ec8b3bfd76e..9f90f460a28c 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -63,6 +63,7 @@ static bool sev_es_negotiate_protocol(void)
 
 static __always_inline void vc_ghcb_invalidate(struct ghcb *ghcb)
 {
+	ghcb->save.sw_exit_code = 0;
 	memset(ghcb->save.valid_bitmap, 0, sizeof(ghcb->save.valid_bitmap));
 }
 
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 45e212675811..4fa111becc93 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -457,6 +457,11 @@ static __always_inline void sev_es_put_ghcb(struct ghcb_state *state)
 		data->backup_ghcb_active = false;
 		state->ghcb = NULL;
 	} else {
+		/*
+		 * Invalidate the GHCB so a VMGEXIT instruction issued
+		 * from userspace won't appear to be valid.
+		 */
+		vc_ghcb_invalidate(ghcb);
 		data->ghcb_active = false;
 	}
 }
-- 
2.31.0