linux-kernel - Re: [PATCH RESEND v4 7/9] KVM: VMX: Handle SPP induced vmexit and page fault

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Date:   Fri, 23 Aug 2019 08:26:10 +0800
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Yang Weijiang <weijiang.yang@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, sean.j.christopherson@...el.com,
        mst@...hat.com, rkrcmar@...hat.com, jmattson@...gle.com,
        yu.c.zhang@...el.com, alazar@...defender.com
Subject: Re: [PATCH RESEND v4 7/9] KVM: VMX: Handle SPP induced vmexit and
 page fault

On Thu, Aug 22, 2019 at 06:38:41PM +0200, Paolo Bonzini wrote:
> On 22/08/19 15:17, Yang Weijiang wrote:
> > On Tue, Aug 20, 2019 at 09:44:35PM +0800, Yang Weijiang wrote:
> >> On Mon, Aug 19, 2019 at 05:04:23PM +0200, Paolo Bonzini wrote:
> >>> fast_page_fault should never trigger an SPP userspace exit on its own,
> >>> all the SPP handling should go through handle_spp.
> >  Hi, Paolo,
> >  According to the latest SDM(28.2.4), handle_spp only handles SPPT miss and SPPT
> >  misconfig(exit_reason==66), subpage write access violation causes EPT violation,
> >  so have to deal with the two cases into handlers.
> 
> Ok, so this part has to remain, though you do have to save/restore
> PT_SPP_MASK according to the rest of the email.
> 
> Paolo
>
Got it, thanks!
> >>> So I think that when KVM wants to write-protect the whole page
> >>> (wrprot_ad_disabled_spte) it must also clear PT_SPP_MASK; for example it
> >>> could save it in bit 53 (PT64_SECOND_AVAIL_BITS_SHIFT + 1).  If the
> >>> saved bit is set, fast_page_fault must then set PT_SPP_MASK instead of
> >>> PT_WRITABLE_MASK.