Re: [PATCH 1/3] x86/S3: Use percpu_traps_init() rather than opencoding SYSCALL/SYSENTER restoration

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.04.2020 16:59, Andrew Cooper wrote:
> @@ -46,24 +36,13 @@ void restore_rest_processor_state(void)
>      /* Restore full CR4 (inc MCE) now that the IDT is in place. */
>      write_cr4(mmu_cr4_features);
>  
> -    /* Recover syscall MSRs */
> -    wrmsrl(MSR_LSTAR, saved_lstar);
> -    wrmsrl(MSR_CSTAR, saved_cstar);
> -    wrmsrl(MSR_STAR, XEN_MSR_STAR);
> -    wrmsrl(MSR_SYSCALL_MASK, XEN_SYSCALL_MASK);
> +    /* (re)initialise SYSCALL/SYSENTER state, amongst other things. */
> +    percpu_traps_init();

Without tweaks to subarch_percpu_traps_init() this assumes that,
now and going forward, map_domain_page() will work reliably at
this early point of resume. I'm not opposed, i.e.
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
but it would feel less fragile if the redundant re-writing of
the stubs would be skipped in the BSP resume case (I didn't
check whether it's also redundant for APs, but I suspect it's
not, as the stub pages may get allocated anew).

Jan