linux-kernel - [PATCH v2 13/16] KVM: arm64: Run clear-dirty-log under MMU read lock

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri,  2 Jun 2023 09:09:11 -0700
From:   Vipin Sharma <vipinsh@...gle.com>
To:     maz@...nel.org, oliver.upton@...ux.dev, james.morse@....com,
        suzuki.poulose@....com, yuzenghui@...wei.com,
        catalin.marinas@....com, will@...nel.org, chenhuacai@...nel.org,
        aleksandar.qemu.devel@...il.com, tsbogend@...ha.franken.de,
        anup@...infault.org, atishp@...shpatra.org,
        paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, seanjc@...gle.com, pbonzini@...hat.com,
        dmatlack@...gle.com, ricarkol@...gle.com
Cc:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        linux-mips@...r.kernel.org, kvm-riscv@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, linux-kselftest@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vipin Sharma <vipinsh@...gle.com>
Subject: [PATCH v2 13/16] KVM: arm64: Run clear-dirty-log under MMU read lock

Take MMU read lock for clearing dirty logs and use shared page table
walker.

Dirty logs are currently cleared using MMU write locks. This
means vCPUs page faults, which takes MMU read lock,  will
be blocked while dirty logs are being cleared. This causes guest
degradation and especially noticeable on VMs with lot of vCPUs.

Taking MMU read lock will allow vCPUs to execute parallelly and reduces
the impact on vCPUs performance.

Signed-off-by: Vipin Sharma <vipinsh@...gle.com>
---
 arch/arm64/kvm/mmu.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 356dc4131023..7c966f6f1a41 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -74,8 +74,12 @@ static int stage2_apply_range(struct kvm_s2_mmu *mmu, phys_addr_t addr,
 		if (ret)
 			break;
 
-		if (resched && next != end)
-			cond_resched_rwlock_write(&kvm->mmu_lock);
+		if (resched && next != end) {
+			if (flags & KVM_PGTABLE_WALK_SHARED)
+				cond_resched_rwlock_read(&kvm->mmu_lock);
+			else
+				cond_resched_rwlock_write(&kvm->mmu_lock);
+		}
 	} while (addr = next, addr != end);
 
 	return ret;
@@ -1131,11 +1135,11 @@ void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm,
 	phys_addr_t start = (base_gfn +  __ffs(mask)) << PAGE_SHIFT;
 	phys_addr_t end = (base_gfn + __fls(mask) + 1) << PAGE_SHIFT;
 
-	write_lock(&kvm->mmu_lock);
-	lockdep_assert_held_write(&kvm->mmu_lock);
-
-	stage2_wp_range(&kvm->arch.mmu, start, end, 0);
+	read_lock(&kvm->mmu_lock);
+	stage2_wp_range(&kvm->arch.mmu, start, end, KVM_PGTABLE_WALK_SHARED);
+	read_unlock(&kvm->mmu_lock);
 
+	write_lock(&kvm->mmu_lock);
 	/*
 	 * Eager-splitting is done when manual-protect is set.  We
 	 * also check for initially-all-set because we can avoid
-- 
2.41.0.rc0.172.g3f132b7071-goog