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[34.168.104.7]) by smtp.gmail.com with ESMTPSA id l15-20020a17090aec0f00b001f216407204sm11136513pjy.36.2022.08.02.09.38.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Aug 2022 09:38:59 -0700 (PDT) Date: Tue, 2 Aug 2022 16:38:55 +0000 From: Sean Christopherson To: Chao Peng Cc: Wei Wang , "Gupta, Pankaj" , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-doc@vger.kernel.org, qemu-devel@nongnu.org, linux-kselftest@vger.kernel.org, Paolo Bonzini , Jonathan Corbet , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H . Peter Anvin" , Hugh Dickins , Jeff Layton , "J . Bruce Fields" , Andrew Morton , Shuah Khan , Mike Rapoport , Steven Price , "Maciej S . Szmigiero" , Vlastimil Babka , Vishal Annapurve , Yu Zhang , "Kirill A . Shutemov" , luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com, ak@linux.intel.com, david@redhat.com, aarcange@redhat.com, ddutile@redhat.com, dhildenb@redhat.com, Quentin Perret , Michael Roth , mhocko@suse.com, Muchun Song Subject: Re: [PATCH v7 11/14] KVM: Register/unregister the guest private memory regions Message-ID: References: <36e671d2-6b95-8e4f-c2ac-fee4b2670c6e@amd.com> <20220720150706.GB124133@chaop.bj.intel.com> <45ae9f57-d595-f202-abb5-26a03a2ca131@linux.intel.com> <20220721092906.GA153288@chaop.bj.intel.com> <20220725130417.GA304216@chaop.bj.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1659458341; a=rsa-sha256; cv=none; b=YoX0xLpZzzomlf5wq72Z75J+1OvlPH2gRq/DmXHfo46PtGvFvKmylvH93pL4sZyXK96fT6 +p/EzTICf2Kxe6KUaz/N/bDrf22oSFtYH+GEIaI0bcsMyzPv7m8JlvzVC/R6vSJmooheoi O6QBbgMnnrMNcPR4kv2NAWxsDSpIHws= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=DEczoNtV; spf=pass (imf03.hostedemail.com: domain of seanjc@google.com designates 209.85.214.172 as permitted sender) smtp.mailfrom=seanjc@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1659458341; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=YLolmPC/4W6Ekt5KXSGhTlaQ+SvTrN9uL1784FHTktA=; b=d87FDp4mQUTFNpTEG2FOW8c2m8pTg3t0sVf/Zl3dq0ZKSxFdJ9Q7i3JCF5DcakfHMxOmjE MdVjqnT2p84PtLU+oSD+5brMHaI6em1e4jGVI/2lzQE+N069Zpsfi8d1bHhPj8/BY+UjQH YbWbVeqUSibH6kJRCz6pckpF0UVoEKI= X-Rspamd-Server: rspam04 X-Stat-Signature: pz8o6ziqoqjok351u3dd5d5m131ixdwb Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=DEczoNtV; spf=pass (imf03.hostedemail.com: domain of seanjc@google.com designates 209.85.214.172 as permitted sender) smtp.mailfrom=seanjc@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Queue-Id: 6DDAB20109 X-Rspam-User: X-HE-Tag: 1659458341-98477 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Aug 02, 2022, Sean Christopherson wrote: > I think we should avoid UNMAPPABLE even on the KVM side of things for the core > memslots functionality and instead be very literal, e.g. > > KVM_HAS_FD_BASED_MEMSLOTS > KVM_MEM_FD_VALID > > We'll still need KVM_HAS_USER_UNMAPPABLE_MEMORY, but it won't be tied directly to > the memslot. Decoupling the two thingis will require a bit of extra work, but the > code impact should be quite small, e.g. explicitly query and propagate > MEMFILE_F_USER_INACCESSIBLE to kvm_memory_slot to track if a memslot can be private. > And unless I'm missing something, it won't require an additional memslot flag. > The biggest oddity (if we don't also add KVM_MEM_PRIVATE) is that KVM would > effectively ignore the hva for fd-based memslots for VM types that don't support > private memory, i.e. userspace can't opt out of using the fd-based backing, but that > doesn't seem like a deal breaker. Hrm, but basing private memory on top of a generic FD_VALID would effectively require shared memory to use hva-based memslots for confidential VMs. That'd yield a very weird API, e.g. non-confidential VMs could be backed entirely by fd-based memslots, but confidential VMs would be forced to use hva-based memslots. Ignore this idea for now. If there's an actual use case for generic fd-based memory then we'll want a separate flag, fd, and offset, i.e. that support could be added independent of KVM_MEM_PRIVATE.