linux-kernel - Re: [PATCH v4 03/14] X86/nVMX: Update the PML table without mapping and unmapping the page

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Message-ID: <3bc6ea8d-7ffb-5c2b-5429-18dc0e6e135a@redhat.com>
Date:   Mon, 3 Dec 2018 14:10:14 +0100
From:   David Hildenbrand <david@...hat.com>
To:     KarimAllah Ahmed <karahmed@...zon.de>, rkrcmar@...hat.com,
        pbonzini@...hat.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, jmattson@...gle.com
Subject: Re: [PATCH v4 03/14] X86/nVMX: Update the PML table without mapping
 and unmapping the page

On 03.12.18 10:30, KarimAllah Ahmed wrote:
> Update the PML table without mapping and unmapping the page. This also
> avoids using kvm_vcpu_gpa_to_page(..) which assumes that there is a "struct
> page" for guest memory.
> 
> Signed-off-by: KarimAllah Ahmed <karahmed@...zon.de>
> ---
> v1 -> v2:
> - Use kvm_write_guest_page instead of kvm_write_guest (pbonzini)
> - Do not use pointer arithmetic for pml_address (pbonzini)
> ---
>  arch/x86/kvm/vmx.c | 14 +++++---------
>  1 file changed, 5 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 75817cb..6d6dfa9 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -14427,9 +14427,7 @@ static int vmx_write_pml_buffer(struct kvm_vcpu *vcpu)
>  {
>  	struct vmcs12 *vmcs12;
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
> -	gpa_t gpa;
> -	struct page *page = NULL;
> -	u64 *pml_address;
> +	gpa_t gpa, dst;
>  
>  	if (is_guest_mode(vcpu)) {
>  		WARN_ON_ONCE(vmx->nested.pml_full);
> @@ -14449,15 +14447,13 @@ static int vmx_write_pml_buffer(struct kvm_vcpu *vcpu)
>  		}
>  
>  		gpa = vmcs_read64(GUEST_PHYSICAL_ADDRESS) & ~0xFFFull;
> +		dst = vmcs12->pml_address + sizeof(u64) * vmcs12->guest_pml_index;
>  
> -		page = kvm_vcpu_gpa_to_page(vcpu, vmcs12->pml_address);
> -		if (is_error_page(page))
> +		if (kvm_write_guest_page(vcpu->kvm, gpa_to_gfn(dst), &gpa,
> +					 offset_in_page(dst), sizeof(gpa)))
>  			return 0;
>  
> -		pml_address = kmap(page);
> -		pml_address[vmcs12->guest_pml_index--] = gpa;
> -		kunmap(page);
> -		kvm_release_page_clean(page);

So we've written to the page but released it as clean ... shouldn't that
have been kvm_release_page_dirty?

... also, shouldn't there have been a mark_page_dirty() ?
(to mark it dirty for migration?)

Your patch certainly fixes both conditions (if it was in fact broken).
In that case, we should maybe add that to the cover letter.

Reviewed-by: David Hildenbrand <david@...hat.com>

> +		vmcs12->guest_pml_index--;
>  	}
>  
>  	return 0;
> 


-- 

Thanks,

David / dhildenb