linux-kernel - Re: [PATCH] kvm: Map PFN-type memory regions as writable (if possible)

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Date:   Wed, 17 Jan 2018 18:56:40 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     KarimAllah Ahmed <karahmed@...zon.de>, kvm@...r.kernel.org
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kvm: Map PFN-type memory regions as writable (if
 possible)

On 17/01/2018 18:26, KarimAllah Ahmed wrote:
> For EPT-violations that are triggered by a read, the pages are also mapped with
> write permissions (if their memory region is also writable). That would avoid
> getting yet another fault on the same page when a write occurs.
> 
> This optimization only happens when you have a "struct page" backing the memory
> region. So also enable it for memory regions that do not have a "struct page".
> 
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Cc: kvm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: KarimAllah Ahmed <karahmed@...zon.de>
> ---
>  virt/kvm/kvm_main.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 97da45e..0efb089 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1534,6 +1534,8 @@ static kvm_pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
>  			goto retry;
>  		if (r < 0)
>  			pfn = KVM_PFN_ERR_FAULT;
> +		if (writable)
> +			*writable = true;
>  	} else {
>  		if (async && vma_is_valid(vma, write_fault))
>  			*async = true;
> 

Looks good, but it should be in hva_to_pfn_remapped.

Paolo