linux-kernel - Re: [PATCH v2 5/5] KVM: x86: Don't check kvm_rebooting in __kvm_handle_fault_on

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Date:   Fri, 19 Jul 2019 23:41:20 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     "H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/5] KVM: x86: Don't check kvm_rebooting in
 __kvm_handle_fault_on_reboot()

On 19/07/19 22:41, Sean Christopherson wrote:
> Remove the kvm_rebooting check from VMX/SVM instruction exception fixup
> now that kvm_spurious_fault() conditions its BUG() on !kvm_rebooting.
> Because the 'cleanup_insn' functionally is also gone, deferring to
> kvm_spurious_fault() means __kvm_handle_fault_on_reboot() can eliminate
> its .fixup code entirely and have its exception table entry branch
> directly to the call to kvm_spurious_fault().
> 
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 92c59cd923b6..a5ae5562ce0a 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1511,13 +1511,7 @@ asmlinkage void kvm_spurious_fault(void);
>  	"667: \n\t"							\
>  	"call	kvm_spurious_fault \n\t"				\
>  	"668: \n\t"							\
> -	".pushsection .fixup, \"ax\" \n\t"				\
> -	"700: \n\t"							\
> -	"cmpb	$0, kvm_rebooting\n\t"					\
> -	"je	667b \n\t"						\
> -	"jmp	668b \n\t"						\
> -	".popsection \n\t"						\
> -	_ASM_EXTABLE(666b, 700b)
> +	_ASM_EXTABLE(666b, 667b)
>  
>  #define KVM_ARCH_WANT_MMU_NOTIFIER
>  int kvm_unmap_hva_range(struct kvm *kvm, unsigned long start, unsigned long end);
> 

Acked-by: Paolo Bonzini <pbonzini@...hat.com>