linux-kernel - [RFC PATCH v4 23/39] KVM: arm64: VHE: Clear MDCR_EL2.E2PB in vcpu

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Message-Id: <20210825161815.266051-24-alexandru.elisei@arm.com>
Date:   Wed, 25 Aug 2021 17:17:59 +0100
From:   Alexandru Elisei <alexandru.elisei@....com>
To:     maz@...nel.org, james.morse@....com, suzuki.poulose@....com,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        will@...nel.org, linux-kernel@...r.kernel.org
Cc:     Sudeep Holla <sudeep.holla@....com>
Subject: [RFC PATCH v4 23/39] KVM: arm64: VHE: Clear MDCR_EL2.E2PB in vcpu_put()

From: Sudeep Holla <sudeep.holla@....com>

On VHE systems, the kernel executes at EL2 and configures the profiling
buffer to use the EL2&0 translation regime and to trap accesses from the
guest by clearing MDCR_EL2.E2PB. In vcpu_put(), KVM does a bitwise or with
the E2PB mask, preserving its value. This has been correct so far, since
MDCR_EL2.E2B has the same value (0b00) for all VMs, as set by
kvm_arm_setup_mdcr_el2().

However, this will change when KVM enables support for SPE in guests. For
such guests KVM will configure the profiling buffer to use the EL1&0
translation regime, a setting that is obviously undesirable to be preserved
for the host running at EL2. Let's avoid this situation by explicitly
clearing E2PB in vcpu_put().

[ Alexandru E: Reworded commit ]

Signed-off-by: Sudeep Holla <sudeep.holla@....com>
Signed-off-by: Alexandru Elisei <alexandru.elisei@....com>
---
 arch/arm64/kvm/hyp/vhe/switch.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
index b3229924d243..86d4c8c33f3e 100644
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c
@@ -95,9 +95,7 @@ void deactivate_traps_vhe_put(void)
 {
 	u64 mdcr_el2 = read_sysreg(mdcr_el2);

-	mdcr_el2 &= MDCR_EL2_HPMN_MASK |
-		    MDCR_EL2_E2PB_MASK << MDCR_EL2_E2PB_SHIFT |
-		    MDCR_EL2_TPMS;
+	mdcr_el2 &= MDCR_EL2_HPMN_MASK | MDCR_EL2_TPMS;

 	write_sysreg(mdcr_el2, mdcr_el2);

-- 
2.33.0