| From 4a267aa707953a9a73d1f5dc7f894dd9024a92be Mon Sep 17 00:00:00 2001 |
| From: Alexandru Elisei <alexandru.elisei@arm.com> |
| Date: Mon, 27 Jan 2020 10:36:52 +0000 |
| Subject: KVM: arm64: Treat emulated TVAL TimerValue as a signed 32-bit integer |
| |
| 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: |