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Re: [Xen-devel] [PATCH] x86/boot: enable NMIs during cpu_init()
- To: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 23 Oct 2018 11:28:44 +0100
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- Cc: Wei Liu <wei.liu2@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>
- Delivery-date: Tue, 23 Oct 2018 10:28:53 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
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@xxxxxxxxxx>
> ---
> CC: Jan Beulich <jbeulich@xxxxxxxx>
> CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> ---
> 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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