linux-kernel - Re: [PATCH 08/10] KVM/X86: Use kvm_vcpu_map in emulator_cmpxchg

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Date:   Thu, 22 Feb 2018 02:56:05 +0000
From:   "Raslan, KarimAllah" <karahmed@...zon.de>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
CC:     "hpa@...or.com" <hpa@...or.com>,
        "jmattson@...gle.com" <jmattson@...gle.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>
Subject: Re: [PATCH 08/10] KVM/X86: Use kvm_vcpu_map in
 emulator_cmpxchg_emulated

On Wed, 2018-02-21 at 18:47 +0100, KarimAllah Ahmed wrote:
> ... since using kvm_vcpu_gpa_to_page() and kmap() will only work for guest
> memory that has a "struct page".
> 
> Signed-off-by: KarimAllah Ahmed <karahmed@...zon.de>
> ---
>  arch/x86/kvm/x86.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 37f5df9..197a395 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5013,9 +5013,9 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
>  				     unsigned int bytes,
>  				     struct x86_exception *exception)
>  {
> +	struct kvm_host_map map;

"map" here needs to be memset to '0'. Will fix in v2

>  	struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
>  	gpa_t gpa;
> -	struct page *page;
>  	char *kaddr;
>  	bool exchanged;
>  
> @@ -5032,12 +5032,11 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
>  	if (((gpa + bytes - 1) & PAGE_MASK) != (gpa & PAGE_MASK))
>  		goto emul_write;
>  
> -	page = kvm_vcpu_gfn_to_page(vcpu, gpa >> PAGE_SHIFT);
> -	if (is_error_page(page))
> +	if (!kvm_vcpu_map(vcpu, gpa_to_gfn(gpa), &map))
>  		goto emul_write;
>  
> -	kaddr = kmap_atomic(page);
> -	kaddr += offset_in_page(gpa);
> +	kaddr = map.kaddr + offset_in_page(gpa);
> +
>  	switch (bytes) {
>  	case 1:
>  		exchanged = CMPXCHG_TYPE(u8, kaddr, old, new);
> @@ -5054,8 +5053,8 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
>  	default:
>  		BUG();
>  	}
> -	kunmap_atomic(kaddr);
> -	kvm_release_page_dirty(page);
> +
> +	kvm_vcpu_unmap(&map);
>  
>  	if (!exchanged)
>  		return X86EMUL_CMPXCHG_FAILED;
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