Re: [PATCH 08/13] KVM: MMU: fask check whether page is writable

From: Xiao Guangrong
Date: Fri Mar 30 2012 - 01:11:02 EST

On 03/29/2012 11:49 PM, Avi Kivity wrote:

> On 03/29/2012 11:25 AM, Xiao Guangrong wrote:
>> Using PTE_LIST_WRITE_PROTECT bit in rmap store the write-protect status to
>> avoid unnecessary shadow page walking
> Does kvm_set_pte_rmapp() need adjustment?

Yes, in kvm_set_pte_rmapp(), if the page is host write-protected, it will
set this bit:

static void host_page_write_protect(u64 *spte, unsigned long *rmapp)
if (!(*spte & SPTE_HOST_WRITEABLE) &&

It is very useful for fast page fault path to avoid useless shadow
page table waling if KSM is enabled.

>> Also if no shadow page is indirect, the page is write-free
>> + if (!vcpu->kvm->arch.indirect_shadow_pages)
>> + return 0;
>> +
> Best in its own little patch.

Okay, will split it into a little patch.

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