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From: Marc Zyngier <maz@kernel.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org,
	Will Deacon <will@kernel.org>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Keqian Zhu <zhukeqian1@huawei.com>,
	Christoffer Dall <christoffer.dall@arm.com>,
	Jiang Yi <giangyi@amazon.com>, James Morse <james.morse@arm.com>,
	Andrew Scull <ascull@google.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	David Brazdil <dbrazdil@google.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Ard Biesheuvel <ardb@kernel.org>, Fuad Tabba <tabba@google.com>,
	linux-arm-kernel@lists.infradead.org
Subject: [PATCH 09/24] KVM: arm64: Sidestep stage2_unmap_vm() on vcpu reset when S2FWB is supported
Date: Fri, 29 May 2020 17:01:06 +0100	[thread overview]
Message-ID: <20200529160121.899083-10-maz@kernel.org> (raw)
In-Reply-To: <20200529160121.899083-1-maz@kernel.org>

From: Zenghui Yu <yuzenghui@huawei.com>

stage2_unmap_vm() was introduced to unmap user RAM region in the stage2
page table to make the caches coherent. E.g., a guest reboot with stage1
MMU disabled will access memory using non-cacheable attributes. If the
RAM and caches are not coherent at this stage, some evicted dirty cache
line may go and corrupt guest data in RAM.

Since ARMv8.4, S2FWB feature is mandatory and KVM will take advantage
of it to configure the stage2 page table and the attributes of memory
access. So we ensure that guests always access memory using cacheable
attributes and thus, the caches always be coherent.

So on CPUs that support S2FWB, we can safely reset the vcpu without a
heavy stage2 unmapping.

Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200415072835.1164-1-yuzenghui@huawei.com
---
 arch/arm64/kvm/arm.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index ee1b5bba1d08..0ea9a0266d9a 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -983,8 +983,11 @@ static int kvm_arch_vcpu_ioctl_vcpu_init(struct kvm_vcpu *vcpu,
 	/*
 	 * Ensure a rebooted VM will fault in RAM pages and detect if the
 	 * guest MMU is turned off and flush the caches as needed.
+	 *
+	 * S2FWB enforces all memory accesses to RAM being cacheable, we
+	 * ensure that the cache is always coherent.
 	 */
-	if (vcpu->arch.has_run_once)
+	if (vcpu->arch.has_run_once && !cpus_have_const_cap(ARM64_HAS_STAGE2_FWB))
 		stage2_unmap_vm(vcpu->kvm);
 
 	vcpu_reset_hcr(vcpu);
-- 
2.26.2


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  parent reply	other threads:[~2020-05-29 16:04 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-29 16:00 [GIT PULL] KVM/arm64 updates for Linux 5.8 Marc Zyngier
2020-05-29 16:00 ` [PATCH 01/24] KVM: arm64: Move virt/kvm/arm to arch/arm64 Marc Zyngier
2020-05-29 16:00 ` [PATCH 02/24] KVM: arm64: Kill off CONFIG_KVM_ARM_HOST Marc Zyngier
2020-05-29 16:01 ` [PATCH 03/24] KVM: arm64: Update help text Marc Zyngier
2020-05-29 16:01 ` [PATCH 04/24] KVM: arm64: Change CONFIG_KVM to a menuconfig entry Marc Zyngier
2020-05-29 16:01 ` [PATCH 05/24] KVM: arm64: Clean up kvm makefiles Marc Zyngier
2020-05-29 16:01 ` [PATCH 06/24] KVM: arm64: Simplify __kvm_timer_set_cntvoff implementation Marc Zyngier
2020-05-29 16:01 ` [PATCH 07/24] KVM: arm64: Use cpus_have_final_cap for has_vhe() Marc Zyngier
2020-05-29 16:01 ` [PATCH 08/24] KVM: Fix spelling in code comments Marc Zyngier
2020-05-29 16:01 ` Marc Zyngier [this message]
2020-05-29 16:01 ` [PATCH 10/24] KVM: arm/arm64: Release kvm->mmu_lock in loop to prevent starvation Marc Zyngier
2020-05-29 16:01 ` [PATCH 11/24] KVM: arm64: Clean up the checking for huge mapping Marc Zyngier
2020-05-29 16:01 ` [PATCH 12/24] KVM: arm64: Unify handling THP backed host memory Marc Zyngier
2020-05-29 16:01 ` [PATCH 13/24] KVM: arm64: Support enabling dirty log gradually in small chunks Marc Zyngier
2020-05-29 16:01 ` [PATCH 14/24] KVM: arm64: Make KVM_CAP_MAX_VCPUS compatible with the selected GIC version Marc Zyngier
2020-05-29 16:01 ` [PATCH 15/24] KVM: arm64: Clean up cpu_init_hyp_mode() Marc Zyngier
2020-05-29 16:01 ` [PATCH 16/24] KVM: arm64: Fix incorrect comment on kvm_get_hyp_vector() Marc Zyngier
2020-05-29 16:01 ` [PATCH 17/24] KVM: arm64: Remove obsolete kvm_virt_to_phys abstraction Marc Zyngier
2020-05-29 16:01 ` [PATCH 18/24] KVM: arm64: vgic-v3: Take cpu_if pointer directly instead of vcpu Marc Zyngier
2020-05-29 16:01 ` [PATCH 19/24] KVM: arm64: Refactor vcpu_{read,write}_sys_reg Marc Zyngier
2020-05-29 16:01 ` [PATCH 20/24] KVM: arm64: Add missing reset handlers for PMU emulation Marc Zyngier
2020-05-29 16:01 ` [PATCH 21/24] KVM: arm64: Move sysreg reset check to boot time Marc Zyngier
2020-05-29 16:01 ` [PATCH 22/24] KVM: arm64: Don't use empty structures as CPU reset state Marc Zyngier
2020-05-29 16:01 ` [PATCH 23/24] KVM: arm64: Parametrize exception entry with a target EL Marc Zyngier
2020-05-29 16:01 ` [PATCH 24/24] KVM: arm64: Drop obsolete comment about sys_reg ordering Marc Zyngier
2020-06-01  8:27 ` [GIT PULL] KVM/arm64 updates for Linux 5.8 Paolo Bonzini

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