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Wed, 01 Nov 2023 15:34:59 -0700 (PDT) Date: Wed, 1 Nov 2023 15:34:58 -0700 In-Reply-To: <4ca2253d-276f-43c5-8e9f-0ded5d5b2779@redhat.com> 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> Message-ID: Subject: Re: [PATCH v13 17/35] KVM: Add transparent hugepage support for dedicated guest memory From: Sean Christopherson To: Paolo Bonzini 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?Q?Micka=C3=ABl_Sala=C3=BCn?=" , Vlastimil Babka , Vishal Annapurve , Ackerley Tng , Maciej Szmigiero , David Hildenbrand , Quentin Perret , Michael Roth , Wang , Liam Merwick , Isaku Yamahata , "Kirill A . Shutemov" Content-Type: text/plain; charset="us-ascii" X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 8ACD0C0015 X-Stat-Signature: asky5t11zwu13xcsq474abge7rz3rdiw X-Rspam-User: X-HE-Tag: 1698878100-445294 X-HE-Meta: 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 J9ydbHNq Q5JjUEpyerJjiULfelmnXWT+hZGKeGmIoGxS1N0zOkq6gVMxnUluLLpY9ncHjBlFpusld1k2E9nhrO864zk4iX+QXgf48jQKLILW9P+0e3ufk6jaJRr0QpUBJAQMBSVIS4LDA1HnziQ5QokJLahV/v6jUSFxTDw1Pbmz6jNipJJOOnu1aszjvDhSrzHFCkAKRJRN+zLRwnkHkO6otX+uEDyBhJHnXp6L4IU425FSAmES1sOYj4lmxsZOWR+CR9DQDmcieouYrMTjEII54mBM9KBH55i1ZU+4RlxWP728a+lza8Y3Qv7UBZRF3TPzbpvBa411VKq7bjbP9hf1yPYBglTrk7KqUgzAx39NI5BzVt/P2N78qv8QHr4WKjRgU/EiCYC+mPq+r2Okx3TV/kG4MbOpCjRIUNTEcK1JjpC8VMquywgMeBtfyqUgFt+cr00ykq84bj9EW/h6hLak6hTVadhLhuI07HcV9X3U8xMzY0s93g760Ch1zfSdEveHvVFcvI4Acq0XzorDnTQdXF0gklou5e5YFRzGoHfEFLoU8OUhXSHHitSwf6D+9RLx7OGgVnOgamQjbbAjyytGgwju4Z8tMXAhrM0ofeZXx1XPROMOCXZ9pIJWLFk5d0xDYFCPc6VhrPxjPp8sFYU2SJIvGcfwHDw== 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 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_GUEST_MEMFD_USE_HUGEPAGES > > > > or KVM_GUEST_MEMFD_HUGEPAGES flag, but I wanted the name to convey that KVM doesn't > > > > (yet) guarantee hugepages. I.e. KVM_GUEST_MEMFD_ALLOW_HUGEPAGE is 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_HUGEPAGE. > > > I think that the current patch is fine, but I will adjust it to always > > > allow the flag, and to make the size check even if !CONFIG_TRANSPARENT_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 behavior 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_create_guest_memfd *args) > { > loff_t size = args->size; > u64 flags = args->flags; > - u64 valid_flags = 0; > - > - if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) > - valid_flags |= KVM_GUEST_MEMFD_ALLOW_HUGEPAGE; > + u64 valid_flags = KVM_GUEST_MEMFD_ALLOW_HUGEPAGE; > if (flags & ~valid_flags) > return -EINVAL; > @@ -441,11 +438,9 @@ int kvm_gmem_create(struct kvm *kvm, struct kvm_create_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_HUGEPAGE=y. #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; }) ... > return __kvm_gmem_create(kvm, size, flags); > } > > Paolo >