linux-kernel - Re: [PATCH] KVM: x86/mmu: Avoid mixing gpa_t with gfn_t in walk_addr

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Message-ID: <fe5b461e-795f-332f-48fe-58fc39fd1ae0@redhat.com>
Date:   Mon, 22 Jun 2020 19:04:53 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86/mmu: Avoid mixing gpa_t with gfn_t in
 walk_addr_generic()

On 22/06/20 17:14, Vitaly Kuznetsov wrote:
> translate_gpa() returns a GPA, assigning it to 'real_gfn' seems obviously
> wrong. There is no real issue because both 'gpa_t' and 'gfn_t' are u64 and
> we don't use the value in 'real_gfn' as a GFN, we do
> 
>  real_gfn = gpa_to_gfn(real_gfn);
> 
> instead. 'If you see a "buffalo" sign on an elephant's cage, do not trust
> your eyes', but let's fix it for good.
> 
> No functional change intended.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/mmu/paging_tmpl.h | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
> index a6d484ea110b..58234bfaca07 100644
> --- a/arch/x86/kvm/mmu/paging_tmpl.h
> +++ b/arch/x86/kvm/mmu/paging_tmpl.h
> @@ -360,7 +360,6 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
>  	++walker->level;
>  
>  	do {
> -		gfn_t real_gfn;
>  		unsigned long host_addr;
>  
>  		pt_access = pte_access;
> @@ -375,7 +374,7 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
>  		walker->table_gfn[walker->level - 1] = table_gfn;
>  		walker->pte_gpa[walker->level - 1] = pte_gpa;
>  
> -		real_gfn = mmu->translate_gpa(vcpu, gfn_to_gpa(table_gfn),
> +		real_gpa = mmu->translate_gpa(vcpu, gfn_to_gpa(table_gfn),
>  					      nested_access,
>  					      &walker->fault);
>  
> @@ -389,12 +388,10 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
>  		 * information to fix the exit_qualification or exit_info_1
>  		 * fields.
>  		 */
> -		if (unlikely(real_gfn == UNMAPPED_GVA))
> +		if (unlikely(real_gpa == UNMAPPED_GVA))
>  			return 0;
>  
> -		real_gfn = gpa_to_gfn(real_gfn);
> -
> -		host_addr = kvm_vcpu_gfn_to_hva_prot(vcpu, real_gfn,
> +		host_addr = kvm_vcpu_gfn_to_hva_prot(vcpu, gpa_to_gfn(real_gpa),
>  					    &walker->pte_writable[walker->level - 1]);
>  		if (unlikely(kvm_is_error_hva(host_addr)))
>  			goto error;
> 

Queued, thanks.

Paolo