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From: Yang Weijiang <weijiang.yang@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Yang Weijiang <weijiang.yang@intel.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	sean.j.christopherson@intel.com, mst@redhat.com,
	rkrcmar@redhat.com, jmattson@google.com, yu.c.zhang@intel.com,
	alazar@bitdefender.com
Subject: Re: [PATCH RESEND v4 7/9] KVM: VMX: Handle SPP induced vmexit and page fault
Date: Tue, 20 Aug 2019 21:44:35 +0800
Message-ID: <20190820134435.GE4828@local-michael-cet-test.sh.intel.com> (raw)
In-Reply-To: <fb6cd8b4-eee9-6e58-4047-550811bffd58@redhat.com>

On Mon, Aug 19, 2019 at 05:04:23PM +0200, Paolo Bonzini wrote:
> On 19/08/19 16:43, Paolo Bonzini wrote:
> >> +			/*
> >> +			 * Record write protect fault caused by
> >> +			 * Sub-page Protection, let VMI decide
> >> +			 * the next step.
> >> +			 */
> >> +			if (spte & PT_SPP_MASK) {
> > Should this be "if (spte & PT_WRITABLE_MASK)" instead?  That is, if the
> > page is already writable, the fault must be an SPP fault.
> 
> Hmm, no I forgot how SPP works; still, this is *not* correct.  For
> example, if SPP marks part of a page as read-write, but KVM wants to
> write-protect the whole page for access or dirty tracking, that should
> not cause an SPP exit.
> 
> 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.
Sure, will change the processing flow.

> On re-entry this will cause an SPP vmexit;
> fast_page_fault should never trigger an SPP userspace exit on its own,
> all the SPP handling should go through handle_spp.
> 
> Paolo

  reply index

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-14  7:03 [PATCH RESEND v4 0/9] Enable Sub-page Write Protection Support Yang Weijiang
2019-08-14  7:03 ` [PATCH RESEND v4 1/9] Documentation: Introduce EPT based Subpage Protection Yang Weijiang
2019-08-14  7:03 ` [PATCH RESEND v4 2/9] KVM: VMX: Add control flags for SPP enabling Yang Weijiang
2019-08-14  7:03 ` [PATCH RESEND v4 3/9] KVM: VMX: Implement functions for SPPT paging setup Yang Weijiang
2019-08-14  7:03 ` [PATCH RESEND v4 4/9] KVM: VMX: Introduce SPP access bitmap and operation functions Yang Weijiang
2019-08-14  7:03 ` [PATCH RESEND v4 5/9] KVM: VMX: Add init/set/get functions for SPP Yang Weijiang
2019-08-14 12:43   ` Vitaly Kuznetsov
2019-08-14 14:34     ` Yang Weijiang
2019-08-15 13:43     ` Yang Weijiang
2019-08-15 14:03       ` Vitaly Kuznetsov
2019-08-19 14:06         ` Yang Weijiang
2019-08-15 16:25       ` Jim Mattson
2019-08-15 16:38         ` Sean Christopherson
2019-08-16 13:31           ` Yang Weijiang
2019-08-16 18:19             ` Jim Mattson
2019-08-19  2:08               ` Yang Weijiang
2019-08-19 15:15                 ` Paolo Bonzini
2019-08-20 12:33                   ` Yang Weijiang
2019-08-19 15:05   ` Paolo Bonzini
2019-08-20 12:36     ` Yang Weijiang
2019-08-19 15:13   ` Paolo Bonzini
2019-08-20 13:09     ` Yang Weijiang
2019-08-14  7:04 ` [PATCH RESEND v4 6/9] KVM: VMX: Introduce SPP user-space IOCTLs Yang Weijiang
2019-08-14  7:04 ` [PATCH RESEND v4 7/9] KVM: VMX: Handle SPP induced vmexit and page fault Yang Weijiang
2019-08-19 14:43   ` Paolo Bonzini
2019-08-19 15:04     ` Paolo Bonzini
2019-08-20 13:44       ` Yang Weijiang [this message]
2019-08-22 13:17         ` Yang Weijiang
2019-08-22 16:38           ` Paolo Bonzini
2019-08-23  0:26             ` Yang Weijiang
2019-08-14  7:04 ` [PATCH RESEND v4 8/9] KVM: MMU: Enable Lazy mode SPPT setup Yang Weijiang
2019-08-19 14:46   ` Paolo Bonzini
2019-08-20 13:12     ` Yang Weijiang
2019-09-04 13:49       ` Yang Weijiang
2019-09-09 17:10         ` Paolo Bonzini
2019-09-11  0:23           ` Yang Weijiang
2019-08-14  7:04 ` [PATCH RESEND v4 9/9] KVM: MMU: Handle host memory remapping and reclaim Yang Weijiang
2019-08-14 12:36 ` [PATCH RESEND v4 0/9] Enable Sub-page Write Protection Support Paolo Bonzini
2019-08-14 14:02   ` Yang Weijiang
2019-08-14 14:06     ` Paolo Bonzini

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