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

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Date:   Thu, 22 Aug 2019 18:38:41 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     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 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

>>> 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.