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[142.167.56.70]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6fac6d5b139sm2637706d6.53.2025.05.28.17.51.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 May 2025 17:51:47 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1uKRUp-00000000qrb-1bN9; Wed, 28 May 2025 21:51:47 -0300 Date: Wed, 28 May 2025 21:51:47 -0300 From: Jason Gunthorpe To: Alex Williamson Cc: David Hildenbrand , lizhe.67@bytedance.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, muchun.song@linux.dev Subject: Re: [PATCH v3] vfio/type1: optimize vfio_pin_pages_remote() for huge folio Message-ID: <20250529005147.GC192517@ziepe.ca> References: <20250520070020.6181-1-lizhe.67@bytedance.com> <3f51d180-becd-4c0d-a156-7ead8a40975b@redhat.com> <20250520162125.772d003f.alex.williamson@redhat.com> <20250521105512.4d43640a.alex.williamson@redhat.com> <20250526201955.GI12328@ziepe.ca> <20250527135252.7a7cfe21.alex.williamson@redhat.com> <20250527234627.GB146260@ziepe.ca> <20250528140941.151b2f70.alex.williamson@redhat.com> 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: <20250528140941.151b2f70.alex.williamson@redhat.com> On Wed, May 28, 2025 at 02:09:41PM -0600, Alex Williamson wrote: > To be fair to libvirt, we'd really like libvirt to make use of iommufd > whenever it's available, but without feature parity this would break > users. If people ask there should be no issue with making API functionality discoverable with a query command of some kind. Alot of new stuff is already discoverable by invoking an ioctl with bogus arguments and checking for EOPNOTSUPP/ENOTTY. But most likely P2P will use the same ioctl as memfd so it will not work that way. So for now libvirt could assume no P2P support in iommufd. A simple algorithm would be to look for more than 1 VFIO device. Or add an xml "disable P2P" which is a useful thing anyhow. > Zhe, so if you have no dependencies on P2P DMA within your device > assignment VMs, the options above may be useful or at least a data > point for comparison of type1 vs IOMMUFD performance. Thanks, Even if Zhe does have P2P DMA I have a feeling the OOT P2P patch may be workable Jason