[Crash-utility] [PATCH v2] x86_64: VC exception stack support

[Alexey Makhalov]

Linux-5.10 has introduced SEV-ES support. New (5th) exception
stack was added: 'VC_stack'.

'struct exception_stacks' cannot be used to obtain size of
VC stack, as it equals zero there. Try another structure
'struct cea_exception_stacks' first as it represents actual
CPU entry area with valid stack sizes and guard pages.

Added check for the case when VC stack is not mapped.
It happens when SEV-ES is not active or not supported.

Signed-off-by: Alexey Makhalov <amakhalov at vmware.com>
---
 x86_64.c | 29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/x86_64.c b/x86_64.c
index fc05e8a..6160305 100644
--- a/x86_64.c
+++ b/x86_64.c
@@ -1367,6 +1367,7 @@ x86_64_ist_init(void)
 	ulong init_tss;
 	struct machine_specific *ms;
 	struct syment *boot_sp, *tss_sp, *ist_sp;
+	char *exc_stack_struct_name = NULL;
 
         ms = machdep->machspec;
 	if (!(tss_sp = per_cpu_symbol_search("per_cpu__init_tss"))) {
@@ -1442,16 +1443,25 @@ x86_64_ist_init(void)
 		return;
 	}
 
-	if (MEMBER_EXISTS("exception_stacks", "NMI_stack")) {
+	if (MEMBER_EXISTS("cea_exception_stacks", "NMI_stack")) {
+		/* The effective cpu entry area mapping with guard pages. */
+		exc_stack_struct_name = "cea_exception_stacks";
+	} else if (MEMBER_EXISTS("exception_stacks", "NMI_stack")) {
+		/* The exception stacks' physical storage. No guard pages and no VC stack. */
+		exc_stack_struct_name = "exception_stacks";
+	}
+	if (exc_stack_struct_name) {
                 for (i = 0; i < MAX_EXCEPTION_STACKS; i++) {
 			if (STREQ(ms->stkinfo.exception_stacks[i], "DEBUG"))
-				ms->stkinfo.esize[i] = MEMBER_SIZE("exception_stacks", "DB_stack");
+				ms->stkinfo.esize[i] = MEMBER_SIZE(exc_stack_struct_name, "DB_stack");
 			else if (STREQ(ms->stkinfo.exception_stacks[i], "NMI"))
-				ms->stkinfo.esize[i] = MEMBER_SIZE("exception_stacks", "NMI_stack");
+				ms->stkinfo.esize[i] = MEMBER_SIZE(exc_stack_struct_name, "NMI_stack");
 			else if (STREQ(ms->stkinfo.exception_stacks[i], "DOUBLEFAULT"))
-				ms->stkinfo.esize[i] = MEMBER_SIZE("exception_stacks", "DF_stack");
+				ms->stkinfo.esize[i] = MEMBER_SIZE(exc_stack_struct_name, "DF_stack");
 			else if (STREQ(ms->stkinfo.exception_stacks[i], "MCE"))
-				ms->stkinfo.esize[i] = MEMBER_SIZE("exception_stacks", "MCE_stack");
+				ms->stkinfo.esize[i] = MEMBER_SIZE(exc_stack_struct_name, "MCE_stack");
+			else if (STREQ(ms->stkinfo.exception_stacks[i], "VC"))
+				ms->stkinfo.esize[i] = MEMBER_SIZE(exc_stack_struct_name, "VC_stack");
 		}
 		/*
 	 	 *  Adjust the top-of-stack addresses down to the base stack address.
@@ -5092,6 +5102,13 @@ skip_stage:
 			ms->stkinfo.exception_stacks[estack], bt->stackbase);
 		if (!(bt->stackbase)) 
 			goto skip_stage;
+		/* VC stack can be unmapped if SEV-ES is inactive. */
+		if (STREQ(ms->stkinfo.exception_stacks[estack], "VC")) {
+			physaddr_t phys;
+			/* Skip this stack if page is not present. */
+			if (!kvtop(NULL, bt->stackbase, &phys, 0))
+				goto skip_stage;
+		}
 		bt->stackbuf = ms->irqstack;
 		alter_stackbuf(bt);
 		in_nmi_stack = STREQ(ms->stkinfo.exception_stacks[estack], "NMI");
@@ -5373,6 +5390,8 @@ x86_64_exception_stacks_init(void)
 				ms->stkinfo.exception_stacks[ist-1] = "DOUBLEFAULT";
 			if (strstr(buf, "machine"))
 				ms->stkinfo.exception_stacks[ist-1] = "MCE";
+			if (strstr(buf, "vmm"))
+				ms->stkinfo.exception_stacks[ist-1] = "VC";
 		}
 	}
 
-- 
2.11.0