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Fri, 27 Feb 2026 09:08:16 -0800 (PST) MIME-Version: 1.0 References: <20260129212510.967611-1-dmatlack@google.com> <20260129212510.967611-11-dmatlack@google.com> <20260226170030.5a938c74@shazbot.org> <20260227084658.3767d801@shazbot.org> In-Reply-To: <20260227084658.3767d801@shazbot.org> From: David Matlack Date: Fri, 27 Feb 2026 09:07:48 -0800 X-Gm-Features: AaiRm519T9RurPcNiWyO80VEVhcFvT0_H9lBfATMd1KVW4QtGFBpubzCvVI4oqQ Message-ID: Subject: Re: [PATCH v2 10/22] vfio/pci: Skip reset of preserved device after Live Update To: Alex Williamson Cc: Adithya Jayachandran , Alexander Graf , Alex Mastro , Alistair Popple , Andrew Morton , Ankit Agrawal , Bjorn Helgaas , Chris Li , David Rientjes , Jacob Pan , Jason Gunthorpe , Jason Gunthorpe , Jonathan Corbet , Josh Hilke , Kevin Tian , kexec@lists.infradead.org, kvm@vger.kernel.org, Leon Romanovsky , Leon Romanovsky , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, Lukas Wunner , =?UTF-8?Q?Micha=C5=82_Winiarski?= , Mike Rapoport , Parav Pandit , Pasha Tatashin , Pranjal Shrivastava , Pratyush Yadav , Raghavendra Rao Ananta , Rodrigo Vivi , Saeed Mahameed , Samiullah Khawaja , Shuah Khan , =?UTF-8?Q?Thomas_Hellstr=C3=B6m?= , Tomita Moeko , Vipin Sharma , Vivek Kasireddy , William Tu , Yi Liu , Zhu Yanjun Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 510B74000D X-Stat-Signature: h5b9jwdkfinoy46gz61fgfcd4b8jutzd X-Rspam-User: X-HE-Tag: 1772212099-565897 X-HE-Meta: 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 N5qNRbhf qNDif56fzW/+8AN7ZDtU8QhL1NFEFif7Apx6CCDXq2W1PftK/e2swPEhsK5+m07/kkIqrQFie+aOvI+B1kRHHYyLgD69yeBH61UgDRkSjsYbPVKkQDbZDKqfSXBPLiBe5smEXVRjkPxIXXyxl2t/8jk0kpYsUV+5IyxOM/Ja5LBof5PqBJ/Hue3ZpE2Hcwu40DnbDjmSQPJvHn01tcq7e4Ru++w0QAJa3G8TnQhs3oRJKJ8qYL8gS4UYJkdu+djU8yPAOj/zY6B6Tc29hCOJxuIuc6OiabJRePL0qTFpm56PjoC7JlrFyta775ipG0dEwjZ1y Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Feb 27, 2026 at 7:47=E2=80=AFAM Alex Williamson = wrote: > > On Fri, 27 Feb 2026 00:51:18 +0000 > David Matlack wrote: > > > On 2026-02-26 05:00 PM, Alex Williamson wrote: > > > On Thu, 29 Jan 2026 21:24:57 +0000 > > > David Matlack wrote: > > > > > > > > - vdev->reset_works =3D !ret; > > > > pci_save_state(pdev); > > > > vdev->pci_saved_state =3D pci_store_saved_state(pdev); > > > > > > Isn't this a problem too? In the first kernel we store the initial, > > > post reset state of the device, now we're storing some arbitrary stat= e. > > > This is the state we're restore when the device is closed. > > > > The previous kernel resets the device and restores it back to its > > post reset state in vfio_pci_liveupdate_freeze() before handing off > > control to the next kernel. So my intention here is that VFIO will > > receive the device in that state, allowing it to call > > pci_store_saved_state() here to capture the post reset state of the > > device again. > > > > Eventually we want to drop the reset in vfio_pci_liveupdate_freeze() an= d > > preserve vdev->pci_saved_state across the Live Update. But I was hoping > > to add that in a follow up series to avoid this one getting too long. > > I appreciate reviewing this in smaller chunks, but how does userspace > know whether the kernel contains a stub implementation of liveupdate or > behaves according to the end goal? Would a new VFIO_DEVICE_INFO_CAP be a good way to communicate this information to userspace? > Also, didn't we violate our own contract in this patch by adding the > reset_works field to the serialization data without updating the > compatibility string? Thanks, Yes, I will fix that in v3.