From: Alexandru Elisei alexandru.elisei@arm.com
commit 4a267aa707953a9a73d1f5dc7f894dd9024a92be upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- virt/kvm/arm/arch_timer.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- 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 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 k { 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: