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Fri, 14 Mar 2025 11:32:10 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHscSVLDkbW24B9zbK0LGwRDEEXA7mFC28oFGsGZvhR+c2wtyNhUM9wN90pI1MPGQwzkAu4dQ== X-Received: by 2002:a05:6214:29ed:b0:6e8:feb2:bad9 with SMTP id 6a1803df08f44-6eaeaaac26fmr45881066d6.30.1741977129812; Fri, 14 Mar 2025 11:32:09 -0700 (PDT) Received: from x1.local ([85.131.185.92]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6eade231261sm26870036d6.30.2025.03.14.11.32.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 14 Mar 2025 11:32:08 -0700 (PDT) Date: Fri, 14 Mar 2025 14:32:05 -0400 From: Peter Xu To: Nikita Kalyazin Cc: James Houghton , akpm@linux-foundation.org, pbonzini@redhat.com, shuah@kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, david@redhat.com, ryan.roberts@arm.com, quic_eberman@quicinc.com, graf@amazon.de, jgowans@amazon.com, roypat@amazon.co.uk, derekmn@amazon.com, nsaenz@amazon.es, xmarcalx@amazon.com Subject: Re: [RFC PATCH 0/5] KVM: guest_memfd: support for uffd missing Message-ID: References: <9e7536cc-211d-40ca-b458-66d3d8b94b4d@amazon.com> <7c304c72-1f9c-4a5a-910b-02d0f1514b01@amazon.com> <69dc324f-99fb-44ec-8501-086fe7af9d0d@amazon.com> <507e6ad7-2e28-4199-948a-4001e0d6f421@amazon.com> <24528be7-8f7a-4928-8bca-5869cf14eace@amazon.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <24528be7-8f7a-4928-8bca-5869cf14eace@amazon.com> On Fri, Mar 14, 2025 at 05:12:35PM +0000, Nikita Kalyazin wrote: > Yes, I was thinking about MADV_POPULATE_WRITE as well, but AFAIK it isn't > available in guest_memfd, at least with direct map removed due to [1] being > updated in [2]: I see, so GUP is no-go. IIUC the userapp can also prefault by writing zeros in a loop after mmap(). Thanks, -- Peter Xu