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AJvYcCU4ajoreyb8mmCTnMM/+0AQlWupsMEovL9Gs1rjA7mHGLJiBEarwZP0jQb02DcLm+HcZw4BA1oD2FPiYNGPLmEla/c= X-Gm-Message-State: AOJu0YwAQlkLeaPsy07YEUyL+jLcOzHi5eckgG+ry46etgf3IRcfLZCV onRYftbcNYAIDAdM69QepBz2RxW1q1sDZJyc8dYLXS3rlzPJ5qedu/BOC24dr+kyd4aj12AEnjV c7Bv+LKkYZbB7Jk/pHw== X-Google-Smtp-Source: AGHT+IFSnjz7OFMOWeVI0MI1apHPovJ16H+bOSMdUdDO7KbUX1eLZ6QqkPj6sVplMDT0O6FTB3I8hMUTstLZ6+/c X-Received: from jthoughton.c.googlers.com ([fda3:e722:ac3:cc00:14:4d90:c0a8:2a4f]) (user=jthoughton job=sendgmr) by 2002:a05:690c:6010:b0:61a:e7f7:a4cc with SMTP id 00721157ae682-62a08dd7631mr39296497b3.4.1717005922981; Wed, 29 May 2024 11:05:22 -0700 (PDT) Date: Wed, 29 May 2024 18:05:09 +0000 In-Reply-To: <20240529180510.2295118-1-jthoughton@google.com> Mime-Version: 1.0 References: <20240529180510.2295118-1-jthoughton@google.com> X-Mailer: git-send-email 2.45.1.288.g0e0cd299f1-goog Message-ID: <20240529180510.2295118-7-jthoughton@google.com> Subject: [PATCH v4 6/7] KVM: arm64: Relax locking for kvm_test_age_gfn and kvm_age_gfn From: James Houghton To: Andrew Morton , Paolo Bonzini Cc: Albert Ou , Ankit Agrawal , Anup Patel , Atish Patra , Axel Rasmussen , Bibo Mao , Catalin Marinas , David Matlack , David Rientjes , Huacai Chen , James Houghton , James Morse , Jonathan Corbet , Marc Zyngier , Michael Ellerman , Nicholas Piggin , Oliver Upton , Palmer Dabbelt , Paul Walmsley , Raghavendra Rao Ananta , Ryan Roberts , Sean Christopherson , Shaoqin Huang , Shuah Khan , Suzuki K Poulose , Tianrui Zhao , Will Deacon , Yu Zhao , Zenghui Yu , kvm-riscv@lists.infradead.org, kvm@vger.kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, loongarch@lists.linux.dev Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: E04B540002 X-Stat-Signature: fspz1qa7msynoy4iki3jsjheq8e6ugxx X-HE-Tag: 1717005923-623617 X-HE-Meta: U2FsdGVkX18UDltx4Stb1exRUi61cujkkP8zJsqe6bWBQHqZFsneIUsE5psFLKkLMXie6EbiDyQDMbKVnLUFt/wV/Y7jyN074Yr0eXNaadW5wuw5ga9saQw5LkWCGlCGxbXxvjTNVuLH0uXmzd2x7BUA7XkZO2w3x2Kptl+mHh+WjxiTste3+4UnLc1OoE9KgakN5cIJVCtIIszlJ9Q/PpyaJGAIhBE8WjZ+0+WWNytqls0PNCTCnnBxOD70+uMEFZSNdhhzCAB9QaoRhE3t9HinlWWjlhp7149lDe/ariK6/lH1hEX5Sr4A2fXzVEYjbc33DEVKgl0MlvOGZou5NOFNEA6QUFMf4ACMgLjsbH70VT5jMAP5hLgIGiMl3TpkpnCmhi7rfQ6pYC9+hnh182Il38JwAuvlnzO1qn7agUIwE/vbWqf9twj3Dwu1q2jFVoZeTe0yWmv5wcMbVLlJedVttKh4kAyIHSBhfCAU4OBe1t1UnRMdtA1+exXTMP9NsUGPNIavwHBzaRzLNLokG//7vPVFzeUkvwl3EvvB7U+icv4cwvmd6HA541ZWGYCRji0TSZrNi1KNL82r3NQdf/kLrtO5AOQ2IdDLZBkO+HL7CbD3C3Yc0xPsBmJkaBXUisoFNv1D4T3U5Ku+D4WC4QWlUVRUGgSboRrWDKlDbxVrIlkx/xr/00pypy0um9T8JTvZzVS6cdtif/xWntWrlgIWdU78NhkYXfEucbhoxL6dwpAZMS9R1NymMaXh4HWKQXPRu04QbKhA5kwfw432rgvSItt7adxeKSqCAcpLk52Ff0YAku4aCqn+yCZgF75cRBMrSGsLTPJWf427hCT59adRfOHdrOUJe5zPtbhQTlI9V+jYDICoyk3XAs/+5tWTOUIODAb1DU0HQQw/+FXxdJKj3X2F535nmf7HS5ZEz4SDvFUyfMGviEoJc/3V7uWcGpdFDae6WFL585Bc2xz clJPJ4z5 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 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: Replace the MMU write locks for read locks. Grabbing the read lock instead of the write lock is safe because the only requirement we have is that the stage-2 page tables do not get deallocated while we are walking them. The stage2_age_walker() callback is safe to race with itself; update the comment to reflect the synchronization change. Signed-off-by: James Houghton --- arch/arm64/kvm/hyp/pgtable.c | 9 ++++----- arch/arm64/kvm/mmu.c | 8 ++++---- 2 files changed, 8 insertions(+), 9 deletions(-) diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c index 9e2bbee77491..eabb07c66a07 100644 --- a/arch/arm64/kvm/hyp/pgtable.c +++ b/arch/arm64/kvm/hyp/pgtable.c @@ -1319,10 +1319,8 @@ static int stage2_age_walker(const struct kvm_pgtable_visit_ctx *ctx, data->young = true; /* - * stage2_age_walker() is always called while holding the MMU lock for - * write, so this will always succeed. Nonetheless, this deliberately - * follows the race detection pattern of the other stage-2 walkers in - * case the locking mechanics of the MMU notifiers is ever changed. + * This walk may not be exclusive; the PTE is permitted to change + * from under us. */ if (data->mkold && !stage2_try_set_pte(ctx, new)) return -EAGAIN; @@ -1345,7 +1343,8 @@ bool kvm_pgtable_stage2_test_clear_young(struct kvm_pgtable *pgt, u64 addr, struct kvm_pgtable_walker walker = { .cb = stage2_age_walker, .arg = &data, - .flags = KVM_PGTABLE_WALK_LEAF, + .flags = KVM_PGTABLE_WALK_LEAF | + KVM_PGTABLE_WALK_SHARED, }; WARN_ON(kvm_pgtable_walk(pgt, addr, size, &walker)); diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index 8337009dde77..40e7427462a7 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c @@ -1775,7 +1775,7 @@ bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range) u64 size = (range->end - range->start) << PAGE_SHIFT; bool young = false; - write_lock(&kvm->mmu_lock); + read_lock(&kvm->mmu_lock); if (!kvm->arch.mmu.pgt) goto out; @@ -1785,7 +1785,7 @@ bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range) size, true); out: - write_unlock(&kvm->mmu_lock); + read_unlock(&kvm->mmu_lock); return young; } @@ -1794,7 +1794,7 @@ bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range) u64 size = (range->end - range->start) << PAGE_SHIFT; bool young = false; - write_lock(&kvm->mmu_lock); + read_lock(&kvm->mmu_lock); if (!kvm->arch.mmu.pgt) goto out; @@ -1804,7 +1804,7 @@ bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range) size, false); out: - write_unlock(&kvm->mmu_lock); + read_unlock(&kvm->mmu_lock); return young; } -- 2.45.1.288.g0e0cd299f1-goog