x86/sev-es: Don't return NULL from sev_es_get_ghcb()

sev_es_get_ghcb() is called from several places but only one of them
checks the return value. The reaction to returning NULL is always the
same: calling panic() and kill the machine.

Instead of adding checks to all call sites, move the panic() into the
function itself so that it will no longer return NULL.

Fixes: 0786138c78e7 ("x86/sev-es: Add a Runtime #VC Exception Handler")
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: stable@vger.kernel.org # v5.10+
Link: https://lkml.kernel.org/r/20210519135251.30093-2-joro@8bytes.org

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 4fa111b..82bced8 100644 (file)
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -203,8 +203,18 @@ static __always_inline struct ghcb *sev_es_get_ghcb(struct ghcb_state *state)
        if (unlikely(data->ghcb_active)) {
                /* GHCB is already in use - save its contents */
 
-               if (unlikely(data->backup_ghcb_active))
-                       return NULL;
+               if (unlikely(data->backup_ghcb_active)) {
+                       /*
+                        * Backup-GHCB is also already in use. There is no way
+                        * to continue here so just kill the machine. To make
+                        * panic() work, mark GHCBs inactive so that messages
+                        * can be printed out.
+                        */
+                       data->ghcb_active        = false;
+                       data->backup_ghcb_active = false;
+
+                       panic("Unable to handle #VC exception! GHCB and Backup GHCB are already in use");
+               }
 
                /* Mark backup_ghcb active before writing to it */
                data->backup_ghcb_active = true;
@@ -1289,7 +1299,6 @@ static __always_inline bool on_vc_fallback_stack(struct pt_regs *regs)
  */
 DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
 {
-       struct sev_es_runtime_data *data = this_cpu_read(runtime_data);
        irqentry_state_t irq_state;
        struct ghcb_state state;
        struct es_em_ctxt ctxt;
@@ -1315,16 +1324,6 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication)
         */
 
        ghcb = sev_es_get_ghcb(&state);
-       if (!ghcb) {
-               /*
-                * Mark GHCBs inactive so that panic() is able to print the
-                * message.
-                */
-               data->ghcb_active        = false;
-               data->backup_ghcb_active = false;
-
-               panic("Unable to handle #VC exception! GHCB and Backup GHCB are already in use");
-       }
 
        vc_ghcb_invalidate(ghcb);
        result = vc_init_em_ctxt(&ctxt, regs, error_code);