Re: [patch 05/13] KVM: MMU: do not write-protect large mappings

[Avi Kivity <avi@qumranet.com>]

Marcelo Tosatti wrote:
> There is not much point in write protecting large mappings. This
> can only happen when a page is shadowed during the window between
> is_largepage_backed and mmu_lock acquision. Zap the entry instead, so
> the next pagefault will find a shadowed page via is_largepage_backed and
> fallback to 4k translations.
>
> Simplifies out of sync shadow.
>
> @@ -1222,6 +1221,14 @@ static void mmu_set_spte(struct kvm_vcpu
>  			if (write_fault)
>  				*ptwrite = 1;
>  		}
> +		/*
> + 		 * Do not create write protected large translations.
> + 		 */
> +		if (largepage && has_wrprotected_page(vcpu->kvm, gfn)) {
> +			spte = shadow_trap_nonpresent_pte;
> +			was_writeble = 0;
> +			*ptwrite = 0;
> +		}
>  	}
>  
>   

Why are you clearing was_writable?


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