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[142.68.128.5]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7b9ac478f0fsm1277723385a.71.2025.01.03.07.19.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Jan 2025 07:19:01 -0800 (PST) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1tTjS0-00000000iwx-2edn; Fri, 03 Jan 2025 11:19:00 -0400 Date: Fri, 3 Jan 2025 11:19:00 -0400 From: Jason Gunthorpe To: David Woodhouse Cc: Thomas Gleixner , Alex Williamson , kvm@vger.kernel.org, quic_bqiang@quicinc.com, kvalo@kernel.org, prestwoj@gmail.com, linux-wireless@vger.kernel.org, ath11k@lists.infradead.org, iommu@lists.linux.dev, kernel@quicinc.com, johannes@sipsolutions.net, jtornosm@redhat.com Subject: Re: [PATCH RFC/RFT] vfio/pci: Create feature to disable MSI virtualization Message-ID: <20250103151900.GE26854@ziepe.ca> References: <20240812170014.1583783-1-alex.williamson@redhat.com> <20240813163053.GK1985367@ziepe.ca> <87r0aspby6.ffs@tglx> <03fdfde8dc05ecce1f1edececf0800d8cb919ac1.camel@infradead.org> <20250103143138.GC26854@ziepe.ca> <432d4304b579c5bd6973628c3c4aaad476627f7b.camel@infradead.org> Precedence: bulk X-Mailing-List: kvm@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: <432d4304b579c5bd6973628c3c4aaad476627f7b.camel@infradead.org> On Fri, Jan 03, 2025 at 02:47:11PM +0000, David Woodhouse wrote: > Probably best for the hypervisor to have some way to *advertise* that > it's handling this though, as guests also might want to run on > hypervisors which don't. If the hypervisor doesn't properly virtualize the device it shouldn't assign it to a VM to start with :\ Intel looked at the question of advertising clean interrupt remapping when trying to virtualize IMS and it didn't seem so great. Bare metal machines need to work, so any test they could think of adding would either fail on bare metal or fail on existing VMs. VMM's have taken the approach of not telling the guest they are in VMs and then also not implementing the bare metal HW behaviors with full fidelity. So we have no way to discover that the VMM is, in fact, emulating broken "hw". Thus we get this push that all kernels need to accomodate the worst VMM behaviors :( Jason