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Wed, 01 Nov 2023 16:17:25 -0700 (PDT) X-Google-Smtp-Source: AGHT+IERW8ZMUKS1oQBttUXGlXfpcF1aXMGz29SltsJOczMO7DdV5tM2YzmJ2Q5mLWwPrzL7OcDPCpWawHIyBUWWBis= X-Received: by 2002:a67:b70e:0:b0:450:8e58:2de4 with SMTP id h14-20020a67b70e000000b004508e582de4mr14946722vsf.7.1698880645133; Wed, 01 Nov 2023 16:17:25 -0700 (PDT) MIME-Version: 1.0 References: <20231027182217.3615211-1-seanjc@google.com> <20231027182217.3615211-18-seanjc@google.com> <7c0844d8-6f97-4904-a140-abeabeb552c1@intel.com> <92ba7ddd-2bc8-4a8d-bd67-d6614b21914f@intel.com> <4ca2253d-276f-43c5-8e9f-0ded5d5b2779@redhat.com> In-Reply-To: From: Paolo Bonzini Date: Thu, 2 Nov 2023 00:17:13 +0100 Message-ID: Subject: Re: [PATCH v13 17/35] KVM: Add transparent hugepage support for dedicated guest memory To: Sean Christopherson Cc: Xiaoyao Li , Marc Zyngier , Oliver Upton , Huacai Chen , Michael Ellerman , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexander Viro , Christian Brauner , "Matthew Wilcox (Oracle)" , Andrew Morton , kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Xu Yilun , Chao Peng , Fuad Tabba , Jarkko Sakkinen , Anish Moorthy , David Matlack , Yu Zhang , Isaku Yamahata , =?UTF-8?B?TWlja2HDq2wgU2FsYcO8bg==?= , Vlastimil Babka , Vishal Annapurve , Ackerley Tng , Maciej Szmigiero , David Hildenbrand , Quentin Perret , Michael Roth , Wang , Liam Merwick , Isaku Yamahata , "Kirill A . Shutemov" X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: 6x6fujjwnqdgyct7pq95cxt8q37d1qpd X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: EC52B18001E X-Rspam-User: X-HE-Tag: 1698880647-660755 X-HE-Meta: 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 XQbBB3Kt 2fRiYV0Yht8B45LxiNElfAQfJk4X5XZVFySwHTCmUG/qfwORM9nMtIjextC3W5kgUNyIRIggEC367ZXUNj99VpsoBUdyZKBMtIdIqkYzxTIIb7bQZb4CuNQHEYuEFw6rZ6i54xYFlGqtxd0soTO50g1+r5PjFnPJnHMfTmDgLeFCrV/xyylC5ExLpBkZTc69jVwCvCKXXuJsGkYrdz8ZPZK190eTTX/hah5lbyz9zOp8L66TiG7iBoduA0i1pEBIGWqt92BjHRgkry0P4kVhN/XEQ+PHHMSOOm6Tf/HCghGQ1ofq6Zs8Rjo/Xrc+xCdIz9FgG/5Uqv+b7eIE= 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: List-Subscribe: List-Unsubscribe: On Wed, Nov 1, 2023 at 11:35=E2=80=AFPM Sean Christopherson wrote: > > On Wed, Nov 01, 2023, Paolo Bonzini wrote: > > On 11/1/23 17:36, Sean Christopherson wrote: > > > > > "Allow" isn't perfect, e.g. I would much prefer a straight KVM_GU= EST_MEMFD_USE_HUGEPAGES > > > > > or KVM_GUEST_MEMFD_HUGEPAGES flag, but I wanted the name to conve= y that KVM doesn't > > > > > (yet) guarantee hugepages. I.e. KVM_GUEST_MEMFD_ALLOW_HUGEPAGE i= s stronger than > > > > > a hint, but weaker than a requirement. And if/when KVM supports = a dedicated memory > > > > > pool of some kind, then we can add KVM_GUEST_MEMFD_REQUIRE_HUGEPA= GE. > > > > I think that the current patch is fine, but I will adjust it to alw= ays > > > > allow the flag, and to make the size check even if !CONFIG_TRANSPAR= ENT_HUGEPAGE. > > > > If hugepages are not guaranteed, and (theoretically) you could have= no > > > > hugepage at all in the result, it's okay to get this result even if= THP is not > > > > available in the kernel. > > > Can you post a fixup patch? It's not clear to me exactly what behavi= or you intend > > > to end up with. > > > > Sure, just this: > > > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > > index 7d1a33c2ad42..34fd070e03d9 100644 > > --- a/virt/kvm/guest_memfd.c > > +++ b/virt/kvm/guest_memfd.c > > @@ -430,10 +430,7 @@ int kvm_gmem_create(struct kvm *kvm, struct kvm_cr= eate_guest_memfd *args) > > { > > loff_t size =3D args->size; > > u64 flags =3D args->flags; > > - u64 valid_flags =3D 0; > > - > > - if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) > > - valid_flags |=3D KVM_GUEST_MEMFD_ALLOW_HUGEPAGE; > > + u64 valid_flags =3D KVM_GUEST_MEMFD_ALLOW_HUGEPAGE; > > if (flags & ~valid_flags) > > return -EINVAL; > > @@ -441,11 +438,9 @@ int kvm_gmem_create(struct kvm *kvm, struct kvm_cr= eate_guest_memfd *args) > > if (size < 0 || !PAGE_ALIGNED(size)) > > return -EINVAL; > > -#ifdef CONFIG_TRANSPARENT_HUGEPAGE > > if ((flags & KVM_GUEST_MEMFD_ALLOW_HUGEPAGE) && > > !IS_ALIGNED(size, HPAGE_PMD_SIZE)) > > return -EINVAL; > > -#endif > > That won't work, HPAGE_PMD_SIZE is valid only for CONFIG_TRANSPARENT_HUGE= PAGE=3Dy. > > #else /* CONFIG_TRANSPARENT_HUGEPAGE */ > #define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; }) > #define HPAGE_PMD_MASK ({ BUILD_BUG(); 0; }) > #define HPAGE_PMD_SIZE ({ BUILD_BUG(); 0; }) Would have caught it when actually testing it, I guess. :) It has to be PMD_SIZE, possibly with #ifdef CONFIG_TRANSPARENT_HUGEPAGE BUILD_BUG_ON(HPAGE_PMD_SIZE !=3D PMD_SIZE); #endif for extra safety. Paolo