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authorAlexandru Elisei <alexandru.elisei@arm.com>2020-01-27 10:36:52 +0000
committerMarc Zyngier <maz@kernel.org>2020-01-28 13:09:31 +0000
commit4a267aa707953a9a73d1f5dc7f894dd9024a92be (patch)
treecfc2b39dc84a54000799f043f76640c4f6dc512e
parentc01d6a18023b94fdd0cb7cf11bbfe769bf71653f (diff)
downloadlinux-4a267aa707953a9a73d1f5dc7f894dd9024a92be.tar.bz2
KVM: arm64: Treat emulated TVAL TimerValue as a signed 32-bit integer
According to the ARM ARM, registers CNT{P,V}_TVAL_EL0 have bits [63:32] RES0 [1]. When reading the register, the value is truncated to the least significant 32 bits [2], and on writes, TimerValue is treated as a signed 32-bit integer [1, 2]. When the guest behaves correctly and writes 32-bit values, treating TVAL as an unsigned 64 bit register works as expected. However, things start to break down when the guest writes larger values, because (u64)0x1_ffff_ffff = 8589934591. but (s32)0x1_ffff_ffff = -1, and the former will cause the timer interrupt to be asserted in the future, but the latter will cause it to be asserted now. Let's treat TVAL as a signed 32-bit register on writes, to match the behaviour described in the architecture, and the behaviour experimentally exhibited by the virtual timer on a non-vhe host. [1] Arm DDI 0487E.a, section D13.8.18 [2] Arm DDI 0487E.a, section D11.2.4 Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com> [maz: replaced the read-side mask with lower_32_bits] Signed-off-by: Marc Zyngier <maz@kernel.org> Fixes: 8fa761624871 ("KVM: arm/arm64: arch_timer: Fix CNTP_TVAL calculation") Link: https://lore.kernel.org/r/20200127103652.2326-1-alexandru.elisei@arm.com
-rw-r--r--virt/kvm/arm/arch_timer.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
index f182b2380345..c6c2a9dde00c 100644
--- a/virt/kvm/arm/arch_timer.c
+++ b/virt/kvm/arm/arch_timer.c
@@ -805,6 +805,7 @@ static u64 kvm_arm_timer_read(struct kvm_vcpu *vcpu,
switch (treg) {
case TIMER_REG_TVAL:
val = timer->cnt_cval - kvm_phys_timer_read() + timer->cntvoff;
+ val &= lower_32_bits(val);
break;
case TIMER_REG_CTL:
@@ -850,7 +851,7 @@ static void kvm_arm_timer_write(struct kvm_vcpu *vcpu,
{
switch (treg) {
case TIMER_REG_TVAL:
- timer->cnt_cval = kvm_phys_timer_read() - timer->cntvoff + val;
+ timer->cnt_cval = kvm_phys_timer_read() - timer->cntvoff + (s32)val;
break;
case TIMER_REG_CTL: