* [PATCH] x86/boot: enable NMIs during cpu_init()
@ 2018-10-23 10:21 Sergey Dyasli
2018-10-23 10:28 ` Andrew Cooper
0 siblings, 1 reply; 2+ messages in thread
From: Sergey Dyasli @ 2018-10-23 10:21 UTC (permalink / raw
To: xen-devel; +Cc: Sergey Dyasli, Wei Liu, Jan Beulich, Andrew Cooper
In certain scenarios, NMIs might be disabled during Xen boot process.
Such situation will cause alternative_instructions() to:
panic("Timed out waiting for alternatives self-NMI to hit");
This bug was originally seen when using tboot to boot Xen.
To prevent this from happening, enable NMIs during cpu_init().
Signed-off-by: Sergey Dyasli <sergey.dyasli@citrix.com>
---
CC: Jan Beulich <jbeulich@suse.com>
CC: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Wei Liu <wei.liu2@citrix.com>
---
xen/arch/x86/cpu/common.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index 057859ab14..09fbd98764 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -819,6 +819,8 @@ void cpu_init(void)
#define CD(register) asm volatile ( "mov %0,%%db" #register : : "r"(0UL) );
CD(0); CD(1); CD(2); CD(3); /* no db4 and db5 */; CD(6); CD(7);
#undef CD
+
+ enable_nmis();
}
void cpu_uninit(unsigned int cpu)
--
2.17.1
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^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] x86/boot: enable NMIs during cpu_init()
2018-10-23 10:21 [PATCH] x86/boot: enable NMIs during cpu_init() Sergey Dyasli
@ 2018-10-23 10:28 ` Andrew Cooper
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Cooper @ 2018-10-23 10:28 UTC (permalink / raw
To: Sergey Dyasli, xen-devel; +Cc: Wei Liu, Jan Beulich
On 23/10/18 11:21, Sergey Dyasli wrote:
> In certain scenarios, NMIs might be disabled during Xen boot process.
> Such situation will cause alternative_instructions() to:
>
> panic("Timed out waiting for alternatives self-NMI to hit");
>
> This bug was originally seen when using tboot to boot Xen.
> To prevent this from happening, enable NMIs during cpu_init().
>
> Signed-off-by: Sergey Dyasli <sergey.dyasli@citrix.com>
> ---
> CC: Jan Beulich <jbeulich@suse.com>
> CC: Andrew Cooper <andrew.cooper3@citrix.com>
> CC: Wei Liu <wei.liu2@citrix.com>
> ---
> xen/arch/x86/cpu/common.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
> index 057859ab14..09fbd98764 100644
> --- a/xen/arch/x86/cpu/common.c
> +++ b/xen/arch/x86/cpu/common.c
> @@ -819,6 +819,8 @@ void cpu_init(void)
> #define CD(register) asm volatile ( "mov %0,%%db" #register : : "r"(0UL) );
> CD(0); CD(1); CD(2); CD(3); /* no db4 and db5 */; CD(6); CD(7);
> #undef CD
> +
I'd add
/* Re-enable NMIs in case our loader (e.g. Tboot) has left them disabled. */
or there is a chance people might try and take these out again.
> + enable_nmis();
> }
>
> void cpu_uninit(unsigned int cpu)
This is actually very late in the BSP path. I'd insert another one
immediately after /* Full exception support from here on in. */ in
__start_xen()
~Andrew
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