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 <[email protected]>
> ---
> CC: Jan Beulich <[email protected]>
> CC: Andrew Cooper <[email protected]>
> CC: Wei Liu <[email protected]>
> ---
> 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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