Re: [Xen-devel] [PATCH 11/13] x86/paravirt: Add paravirt alternatives infrastructure

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

>  #ifdef CONFIG_PARAVIRT
> +/*
> + * Paravirt alternatives are applied much earlier than normal alternatives.
> + * They are only applied when running on a hypervisor.  They replace some
> + * native instructions with calls to pv ops.
> + */
> +void __init apply_pv_alternatives(void)
> +{
> +     setup_force_cpu_cap(X86_FEATURE_PV_OPS);

Not for Xen HVM guests.

> +     apply_alternatives(__pv_alt_instructions, __pv_alt_instructions_end);
> +}


This is a problem (at least for Xen PV guests):
apply_alternatives()->text_poke_early()->local_irq_save()->...'cli'->death.

It might be possible not to turn off/on the interrupts in this
particular case since the guest probably won't be able to handle an
interrupt at this point anyway.


> +
>  void __init_or_module apply_paravirt(struct paravirt_patch_site *start,
>                                    struct paravirt_patch_site *end)
>  {
> diff --git a/arch/x86/kernel/cpu/hypervisor.c 
> b/arch/x86/kernel/cpu/hypervisor.c
> index 4fa90006ac68..17243fe0f5ce 100644
> --- a/arch/x86/kernel/cpu/hypervisor.c
> +++ b/arch/x86/kernel/cpu/hypervisor.c
> @@ -71,6 +71,8 @@ void __init init_hypervisor_platform(void)
>       if (!x86_hyper)
>               return;
>  
> +     apply_pv_alternatives();

Not for Xen PV guests who have already done this.

-boris


> +
>       if (x86_hyper->init_platform)
>               x86_hyper->init_platform();
>  }
>


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