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02 Jul 2020 19:36:05 -0700 From: Sean Christopherson To: Marc Zyngier , Paolo Bonzini , Arnd Bergmann Subject: [PATCH v3 08/21] KVM: x86/mmu: Clean up the gorilla math in mmu_topup_memory_caches() Date: Thu, 2 Jul 2020 19:35:32 -0700 Message-Id: <20200703023545.8771-9-sean.j.christopherson@intel.com> X-Mailer: git-send-email 2.26.0 In-Reply-To: <20200703023545.8771-1-sean.j.christopherson@intel.com> References: <20200703023545.8771-1-sean.j.christopherson@intel.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200702_223615_023788_8177B392 X-CRM114-Status: GOOD ( 15.24 ) X-Spam-Score: -2.3 (--) X-Spam-Report: SpamAssassin version 3.4.4 on merlin.infradead.org summary: Content analysis details: (-2.3 points) pts rule name description ---- ---------------------- -------------------------------------------------- -2.3 RCVD_IN_DNSWL_MED RBL: Sender listed at https://www.dnswl.org/, medium trust [134.134.136.126 listed in list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, Junaid Shahid , Christoffer Dall , Wanpeng Li , kvm@vger.kernel.org, Suzuki K Poulose , Joerg Roedel , Peter Shier , linux-mips@vger.kernel.org, Sean Christopherson , linux-kernel@vger.kernel.org, James Morse , linux-arm-kernel@lists.infradead.org, Ben Gardon , Vitaly Kuznetsov , Peter Feiner , kvmarm@lists.cs.columbia.edu, Julien Thierry , Jim Mattson Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org Clean up the minimums in mmu_topup_memory_caches() to document the driving mechanisms behind the minimums. Now that encountering an empty cache is unlikely to trigger BUG_ON(), it is less dangerous to be more precise when defining the minimums. For rmaps, the logic is 1 parent PTE per level, plus a single rmap, and prefetched rmaps. The extra objects in the current '8 + PREFETCH' minimum came about due to an abundance of paranoia in commit c41ef344de212 ("KVM: MMU: increase per-vcpu rmap cache alloc size"), i.e. it could have increased the minimum to 2 rmaps. Furthermore, the unexpected extra rmap case was killed off entirely by commits f759e2b4c728c ("KVM: MMU: avoid pte_list_desc running out in kvm_mmu_pte_write") and f5a1e9f89504f ("KVM: MMU: remove call to kvm_mmu_pte_write from walk_addr"). For the so called page cache, replace '8' with 2*PT64_ROOT_MAX_LEVEL. The 2x multiplier is needed because the cache is used for both shadow pages and gfn arrays for indirect MMUs. And finally, for page headers, replace '4' with PT64_ROOT_MAX_LEVEL. Note, KVM now supports 5-level paging, i.e. the old minimums that used a baseline derived from 4-level paging were technically wrong. But, KVM always allocates roots in a separate flow, e.g. it's impossible in the current implementation to actually need 5 new shadow pages in a single flow. Use PT64_ROOT_MAX_LEVEL unmodified instead of subtracting 1, as the direct usage is likely more intuitive to uninformed readers, and the inflated minimum is unlikely to affect functionality in practice. Reviewed-by: Ben Gardon Signed-off-by: Sean Christopherson --- arch/x86/kvm/mmu/mmu.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 3d0768e16463..cf02ad93c249 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -1103,14 +1103,17 @@ static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu) { int r; + /* 1 rmap, 1 parent PTE per level, and the prefetched rmaps. */ r = mmu_topup_memory_cache(&vcpu->arch.mmu_pte_list_desc_cache, - 8 + PTE_PREFETCH_NUM); + 1 + PT64_ROOT_MAX_LEVEL + PTE_PREFETCH_NUM); if (r) return r; - r = mmu_topup_memory_cache(&vcpu->arch.mmu_page_cache, 8); + r = mmu_topup_memory_cache(&vcpu->arch.mmu_page_cache, + 2 * PT64_ROOT_MAX_LEVEL); if (r) return r; - return mmu_topup_memory_cache(&vcpu->arch.mmu_page_header_cache, 4); + return mmu_topup_memory_cache(&vcpu->arch.mmu_page_header_cache, + PT64_ROOT_MAX_LEVEL); } static void mmu_free_memory_caches(struct kvm_vcpu *vcpu)