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[34.142.255.199]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2c16629d40asm208599735ad.64.2026.06.09.08.12.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Jun 2026 08:12:20 -0700 (PDT) Date: Tue, 9 Jun 2026 15:12:11 +0000 From: Pranjal Shrivastava To: Jason Gunthorpe Cc: David Matlack , kexec@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, Adithya Jayachandran , Alexander Graf , Alex Williamson , Bjorn Helgaas , Chris Li , David Rientjes , Jacob Pan , Jonathan Corbet , Josh Hilke , Leon Romanovsky , Lukas Wunner , Mike Rapoport , Parav Pandit , Pasha Tatashin , Pratyush Yadav , Saeed Mahameed , Samiullah Khawaja , Shuah Khan , Vipin Sharma , William Tu , Yi Liu Subject: Re: [PATCH v6 08/12] PCI: liveupdate: Inherit ACS flags in incoming preserved devices Message-ID: References: <20260522202410.3104264-1-dmatlack@google.com> <20260522202410.3104264-9-dmatlack@google.com> <20260608181640.GO1962447@nvidia.com> Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260608181640.GO1962447@nvidia.com> On Mon, Jun 08, 2026 at 03:16:40PM -0300, Jason Gunthorpe wrote: > On Mon, Jun 08, 2026 at 10:49:29AM +0000, Pranjal Shrivastava wrote: > > > My point was that a FW exploit can meddle with the bitfields of the > > ACS_CTRL to spoof and mis-report the ACS flags. > > Devices can also ignore the ACS flags. I don't think this is an area > where we should be worrying about devices being actively hostile. I'm wondering what happens if we preserve IOMMU groups across a kexec, but a switch's ACS capability is dropped or the ACS_RR bit gets cleared? The incoming kernel assumes that it's the same ACS cap from the old one Now, the incoming kernel restores the groups assuming they're still isolated, but the hardware no longer enforces it, silently allowing DMAs & breaking isolation? Thanks, Praan