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

[Alexey Makhalov]

Found interesting thing: VC stack is only mapped if SEV-ES is active. VA present in IST, but page is not valid.
Will send v2 shortly.

—Alexey

> On Nov 11, 2020, at 12:26 PM, Alexey Makhalov <amakhalov at vmware.com> wrote:
> 
> 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 zero size stack to avoid stack parsing
> issues.
> 
> Signed-off-by: Alexey Makhalov <amakhalov at vmware.com>
> ---
> x86_64.c | 24 ++++++++++++++++++------
> 1 file changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/x86_64.c b/x86_64.c
> index fc05e8a..ea4a894 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.
> @@ -5090,7 +5100,7 @@ skip_stage:
>                 	ms->stkinfo.esize[estack];
> 		console("x86_64_get_dumpfile_stack_frame: searching %s estack at %lx\n", 
> 			ms->stkinfo.exception_stacks[estack], bt->stackbase);
> -		if (!(bt->stackbase)) 
> +		if (!(bt->stackbase) || !(ms->stkinfo.esize[estack]))
> 			goto skip_stage;
> 		bt->stackbuf = ms->irqstack;
> 		alter_stackbuf(bt);
> @@ -5373,6 +5383,8 @@ 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
>