[PATCH for-4.8] x86/cpu: Reposition stack alignment check

[PATCH for-4.8] x86/cpu: Reposition stack alignment check

[Andrew Cooper]

As identified during review, using BUG_ON() before `lidt` will result in a
triple fault, even on APs.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wei.liu2@citrix.com>
---
 xen/arch/x86/cpu/common.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index 06ee401..16cf001 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -643,11 +643,6 @@ void load_system_tables(void)
 		.limit = (IDT_ENTRIES * sizeof(idt_entry_t)) - 1,
 	};
 
-	/* Bottom-of-stack must be 16-byte aligned! */
-	BUILD_BUG_ON((sizeof(struct cpu_info) -
-		      offsetof(struct cpu_info, guest_cpu_user_regs.es)) & 0xf);
-	BUG_ON(system_state != SYS_STATE_early_boot && (stack_bottom & 0xf));
-
 	/* Main stack for interrupts/exceptions. */
 	tss->rsp0 = stack_bottom;
 	tss->bitmap = IOBMP_INVALID_OFFSET;
@@ -672,6 +667,15 @@ void load_system_tables(void)
 	asm volatile ("lidt %0"  : : "m"  (idtr) );
 	asm volatile ("ltr  %w0" : : "rm" (TSS_ENTRY << 3) );
 	asm volatile ("lldt %w0" : : "rm" (0) );
+
+	/*
+         * Bottom-of-stack must be 16-byte aligned!
+         *
+         * Defer checks until exception support is sufficiently set up.
+         */
+	BUILD_BUG_ON((sizeof(struct cpu_info) -
+		      offsetof(struct cpu_info, guest_cpu_user_regs.es)) & 0xf);
+	BUG_ON(system_state != SYS_STATE_early_boot && (stack_bottom & 0xf));
 }
 
 /*
-- 
2.1.4


_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
https://lists.xen.org/xen-devel

Re: [PATCH for-4.8] x86/cpu: Reposition stack alignment check

[Wei Liu]

On Fri, Nov 25, 2016 at 07:04:51PM +0000, Andrew Cooper wrote:
> As identified during review, using BUG_ON() before `lidt` will result in a
> triple fault, even on APs.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> ---
> CC: Jan Beulich <JBeulich@suse.com>
> CC: Wei Liu <wei.liu2@citrix.com>

On the basis that this is a critical bug fix:

Release-acked-by: Wei Liu <wei.liu2@citrix.com>

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
https://lists.xen.org/xen-devel

Re: [PATCH for-4.8] x86/cpu: Reposition stack alignment check

[Jan Beulich]

>>> On 25.11.16 at 20:04, <andrew.cooper3@citrix.com> wrote:
> As identified during review, using BUG_ON() before `lidt` will result in a
> triple fault, even on APs.

Oh, I did commit v1 instead of v2, sorry.

> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>


_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
https://lists.xen.org/xen-devel

Re: [PATCH for-4.8] x86/cpu: Reposition stack alignment check

[Jan Beulich]

>>> On 25.11.16 at 20:04, <andrew.cooper3@citrix.com> wrote:
> @@ -672,6 +667,15 @@ void load_system_tables(void)
>  	asm volatile ("lidt %0"  : : "m"  (idtr) );
>  	asm volatile ("ltr  %w0" : : "rm" (TSS_ENTRY << 3) );
>  	asm volatile ("lldt %w0" : : "rm" (0) );
> +
> +	/*
> +         * Bottom-of-stack must be 16-byte aligned!
> +         *
> +         * Defer checks until exception support is sufficiently set up.
> +         */

I've applied this right away, correcting the indentation issue here.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
https://lists.xen.org/xen-devel