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[142.162.112.119]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-50744963095sm36791911cf.3.2026.02.26.16.21.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Feb 2026 16:21:06 -0800 (PST) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1vvlbN-00000000pwc-2290; Thu, 26 Feb 2026 20:21:05 -0400 Date: Thu, 26 Feb 2026 20:21:05 -0400 From: Jason Gunthorpe To: Sean Christopherson Cc: Ackerley Tng , Alexey Kardashevskiy , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Kevin Tian , Joerg Roedel , Will Deacon , Robin Murphy , Paolo Bonzini , Steve Sistare , Nicolin Chen , iommu@lists.linux.dev, linux-coco@lists.linux.dev, Dan Williams , Santosh Shukla , "Pratik R . Sampat" , Fuad Tabba , Xu Yilun , "Aneesh Kumar K . V" , michael.roth@amd.com, vannapurve@google.com Subject: Re: [RFC PATCH kernel] iommufd: Allow mapping from KVM's guest_memfd Message-ID: <20260227002105.GC44359@ziepe.ca> References: <20260225075211.3353194-1-aik@amd.com> <20260226190757.GA44359@ziepe.ca> 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: On Thu, Feb 26, 2026 at 02:40:50PM -0800, Sean Christopherson wrote: > > If guestmemfd is fully pinned and cannot free memory outside of > > truncate that may be good enough (though somehow I think that is not > > the case) > > With in-place conversion, PUNCH_HOLE and private=>shared conversions are the only > two ways to partial "remove" memory from guest_memfd, so it may really be that > simple. PUNCH_HOLE can be treated like truncate right? I'm confused though - I thought in-place conversion ment that private<->shared re-used the existing memory allocation? Why does it "remove" memory? Or perhaps more broadly, where is the shared memory kept/accessed in these guest memfd systems? Jason