Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v2 2/3] KVM: x86: fix nested guest live migration with PML
To:     Paolo Bonzini <pbonzini@redhat.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     Vitaly Kuznetsov <vkuznets@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>
References: <1569582943-13476-1-git-send-email-pbonzini@redhat.com>
 <1569582943-13476-3-git-send-email-pbonzini@redhat.com>
From:   Junaid Shahid <junaids@google.com>
Openpgp: preference=signencrypt
Autocrypt: addr=junaids@google.com; keydata=
 mQGNBFyBfSUBDADJpxqPVaO+D+pK2zarR0QwxUAAA7kVV9uPO5iEJXWAmZJJSzeRSoZEEcVg
 hXXQzmYaEn18kA/lDih1/20gr7y0sCupvQwnE0itvLYqyPzmWv93ilkOXnus7CySH2CDINH7
 49+kHhA5YX1TxWBYoAbKxyc/IKHG7h/hsSxCfQhYZimE1hpZUcVx77GD6h2Fbh855c2p8RN8
 D/A+fMkBncrpRgWjpc64bLrZnLGJz+/BB301xA2xhMrllGpgreW6ZmiUEh1/oTWMnEUzADx5
 bzDRSZyw4fUlysAOujmHmJ4B6ORIhYZkyReo2wdHXizsv2lonifygsM8yfBSAOEBez3yDoic
 Yb9qIZoVNlBGFuHJrp4sx41JxFr9EOeHQtbX8O3iy+n8afrBlVPMZiUkEtnsat+LsT5ix2Nk
 mdeY9J5zBwalKEC5zCZ1OfSo9rBLF+pamT/EeCGzatNFY7pyqcOjGvFxloYEKn+D8P0DYFRP
 ny7CeVwLZo43nkaiyRKMeHcAEQEAAbQiSnVuYWlkIFNoYWhpZCA8anVuYWlkc0Bnb29nbGUu
 Y29tPokB1AQTAQoAPhYhBK06Mjqf2kfFM5QUJZzM5LZ0wQJuBQJcgX0lAhsDBQkDwmcABQsJ
 CAcCBhUKCQgLAgQWAgMBAh4BAheAAAoJEJzM5LZ0wQJuwcwMAIKabL0Uv5uk7u6ti+HXf85U
 AFGauxVOWoJHMpK0I2FwuokaumOZDOjAmYvMc9vka6W9CrR0A1LbxIJofFiG8K2cGPxAVWp1
 ozihfXJ4FJneCime741VCdNTlAa5nE7RAppGMuQHjrDI8+oRO5je28UVc8y+neHvgqk3Q1WA
 PbRDTWlnEcdas9GjCMHKb760NLIterenSuuNKIiJraUyA22Hx4F+xIfX7h3tyDnd4x5HGRNg
 Vkji+usAwYSQi9RrVLG2tWKq+Jn2KzmplmmpALsTyMNYWJG7bi7Ler7tNgCpvVcrBjj5Ggo+
 ELmhY56b9EjFT8NjA0vJWT97ulfte9swDpOGxPvACXeRJ+zj+XI9IXet9m6Nj5Jwg9ZROHv7
 FKaupIO0BViiqkuH1je8TQTNbuDaFibvOL5kX90a1ksNKt1kPVfG+oEhhfhDGYHe6corVTkG
 8jyQMogT8fdKxk4BcmHntZKVJgAgD0wlwD1jxWxiANFu0VMVcw/1H81uYrkBjQRcgX0lAQwA
 yYPd+RNEuoUG87by+P8pkbFdATn5Iw9eHE88j9XCTb+kZeckiun3doWKH4FWcD7hDooDBGH2
 lhzx9Qv+cqga4y+lHAONHJRkska/RTf7TLG/363rb/HCHPBOY8FihN57Pewb3ozhtYF/p9/a
 O+hs0NEnqs/lmw1eULp9EuwpyhmbLnWARCG1aviMIGhnB7re7B4i0+VNrMjqVSDPX+iMVy7c
 QJb1T0DtxKjLIg8vZBBaQO/k6R/7Pvuy7Ld0j1MIwDGWZqL4sNiZE8MFgbYq3E7C5lCEtm/5
 GMI4MVppbk/s18yI+HAyHq75bTw1Vh9RKz5RD2Or3UDPrLwjrSEe7+Aw73GY/9MEdmlllcvh
 6TVkYyo2melaffi7aZnfqtRK9n0eF5bdfwo/dU7G89CxSbkMofeobHXobMSJCETVCzkIFjjn
 EBUguMYLhtsxK7NjypX8eYM46wuxVRgHqV6Sf/hYoJkcBa7jJf0epr/dGZHSYF9uq4qIX5ww
 fNqabsu3ABEBAAGJAbwEGAEKACYWIQStOjI6n9pHxTOUFCWczOS2dMECbgUCXIF9JQIbDAUJ
 A8JnAAAKCRCczOS2dMECbt8hC/0QoPTA6kfuCMoKq9uT7sRdM7Zx+y8ug0J63HjhsdEfXoMx
 88qXOG/rRrh99uxgqtr5NgtD3kftAtUcBglhgwJxLwo/WLmCFn/zBTZA4klTLgYqRrDtQvev
 bhzXMcSlBsZWiWPaLpSN6CBxWdxSlMWDwnZhfKMwQhg16tk7sxV/vfHU60ZoeIqKfHV83qg5
 nEbeUprl/vwWv3b7d4PgKCLPEhjPFU/6oWuD4cgrsPNp8xqVZ7BXHpWH0hXcIMV2H3+zV4vj
 dJcBMt0VfEgATMVj6fSTZlh3lRceC/OXza2q0qg2HIT9yxErYIL8YSAFikZPJjkG1Wwv9CTd
 s2WSlTd3YfM2EGcJFP1XFZQKl+vs1Jop+rFjynQB2jX0GP1IG4ab1NYHAVX9ENhIiE97gMLL
 5X/clE5ZjNHVh8p8Ivv4UyZk2pfJxBgg9++M3EXfVuZpP4Rzna4ttKLdB5Ehv7YuGHu8E0n9
 iWogGkOc4UGfcj87Lt9ivHEsVoo/lwCTIiQ=
Organization: Google
Message-ID: <0b6701ed-8eac-1f52-8fdd-c06d2289ce11@google.com>
Date:   Fri, 27 Sep 2019 13:24:37 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.8.0
MIME-Version: 1.0
In-Reply-To: <1569582943-13476-3-git-send-email-pbonzini@redhat.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 9/27/19 4:15 AM, Paolo Bonzini wrote:
> Shadow paging is fundamentally incompatible with the page-modification
> log, because the GPAs in the log come from the wrong memory map.
> In particular, for the EPT page-modification log, the GPAs in the log come
> from L2 rather than L1.  (If there was a non-EPT page-modification log,
> we couldn't use it for shadow paging because it would log GVAs rather
> than GPAs).
> 
> Therefore, we need to rely on write protection to record dirty pages.
> This has the side effect of bypassing PML, since writes now result in an
> EPT violation vmexit.
> 
> This is relatively easy to add to KVM, because pretty much the only place
> that needs changing is spte_clear_dirty.  The first access to the page
> already goes through the page fault path and records the correct GPA;
> it's only subsequent accesses that are wrong.  Therefore, we can equip
> set_spte (where the first access happens) to record that the SPTE will
> have to be write protected, and then spte_clear_dirty will use this
> information to do the right thing.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---

Reviewed-by: Junaid Shahid <junaids@google.com>