Messages in this thread | | | Date | Fri, 06 Apr 2012 01:54:52 +0800 | From | Xiao Guangrong <> | Subject | Re: [PATCH 08/13] KVM: MMU: fask check whether page is writable |
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Hi Avi,
Thanks very much for your review!
Sorry for the delay reply since i was on vacation.
On 04/01/2012 11:52 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 >> >> Also if no shadow page is indirect, the page is write-free >> >> >> @@ -2262,6 +2291,9 @@ static int mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn, >> } >> if (need_unsync) >> kvm_unsync_pages(vcpu, gfn); >> + >> + *rmap &= ~PTE_LIST_WRITE_PROTECT; >> + >> > > So what are the rules for PTE_LIST_WRITE_PROTECT? Is is a cache for the > mmu_need_write_protect? > > I'd like to understand it, I guess it can be set while write protection > is unneeded, and cleared on the next check? >
Yes, it is used as a cache for mmu_need_write_protect.
When the gfn is protected by sync sp or read-only host page we set this bit, and it is be cleared when the sp become unsync or host page becomes writable.
> Maybe split into two functions, one the normal mmu_need_write_protect > (but renamed) and a new mmu_need_write_protect(), with locked and > unlocked variants, calling the old one. >
Okay, i will split it by introducing a new function named mmu_unsync_gfn_sp which checks whether sp can become unsync and unsync sp if it is allowed under the protection of mmu-lock.
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