[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [qemu-xen master] goldfish_rtc: Fix non-atomic read behaviour of TIME_LOW/TIME_HIGH
commit 8380b3a453c38f040e7ca2105418802344cc23d0 Author: Jessica Clarke <jrtc27@xxxxxxxxxx> AuthorDate: Sat Jul 18 01:49:34 2020 +0100 Commit: Alistair Francis <alistair.francis@xxxxxxx> CommitDate: Wed Jul 22 09:39:46 2020 -0700 goldfish_rtc: Fix non-atomic read behaviour of TIME_LOW/TIME_HIGH The specification says: 0x00 TIME_LOW R: Get current time, then return low-order 32-bits. 0x04 TIME_HIGH R: Return high 32-bits from previous TIME_LOW read. ... To read the value, the kernel must perform an IO_READ(TIME_LOW), which returns an unsigned 32-bit value, before an IO_READ(TIME_HIGH), which returns a signed 32-bit value, corresponding to the higher half of the full value. However, we were just returning the current time for both. If the guest is unlucky enough to read TIME_LOW and TIME_HIGH either side of an overflow of the lower half, it will see time be in the future, before jumping backwards on the next read, and Linux currently relies on the atomicity guaranteed by the spec so is affected by this. Fix this violation of the spec by caching the correct value for TIME_HIGH whenever TIME_LOW is read, and returning that value for any TIME_HIGH read. Signed-off-by: Jessica Clarke <jrtc27@xxxxxxxxxx> Reviewed-by: Peter Maydell <peter.maydell@xxxxxxxxxx> Reviewed-by: Richard Henderson <richard.henderson@xxxxxxxxxx> Message-Id: <20200718004934.83174-1-jrtc27@xxxxxxxxxx> Signed-off-by: Alistair Francis <alistair.francis@xxxxxxx> --- hw/rtc/goldfish_rtc.c | 17 ++++++++++++++--- include/hw/rtc/goldfish_rtc.h | 1 + 2 files changed, 15 insertions(+), 3 deletions(-) diff --git a/hw/rtc/goldfish_rtc.c b/hw/rtc/goldfish_rtc.c index 01e9d2b083..6ddd45cce0 100644 --- a/hw/rtc/goldfish_rtc.c +++ b/hw/rtc/goldfish_rtc.c @@ -94,12 +94,22 @@ static uint64_t goldfish_rtc_read(void *opaque, hwaddr offset, GoldfishRTCState *s = opaque; uint64_t r = 0; + /* + * From the documentation linked at the top of the file: + * + * To read the value, the kernel must perform an IO_READ(TIME_LOW), which + * returns an unsigned 32-bit value, before an IO_READ(TIME_HIGH), which + * returns a signed 32-bit value, corresponding to the higher half of the + * full value. + */ switch (offset) { case RTC_TIME_LOW: - r = goldfish_rtc_get_count(s) & 0xffffffff; + r = goldfish_rtc_get_count(s); + s->time_high = r >> 32; + r &= 0xffffffff; break; case RTC_TIME_HIGH: - r = goldfish_rtc_get_count(s) >> 32; + r = s->time_high; break; case RTC_ALARM_LOW: r = s->alarm_next & 0xffffffff; @@ -216,7 +226,7 @@ static const MemoryRegionOps goldfish_rtc_ops = { static const VMStateDescription goldfish_rtc_vmstate = { .name = TYPE_GOLDFISH_RTC, - .version_id = 1, + .version_id = 2, .pre_save = goldfish_rtc_pre_save, .post_load = goldfish_rtc_post_load, .fields = (VMStateField[]) { @@ -225,6 +235,7 @@ static const VMStateDescription goldfish_rtc_vmstate = { VMSTATE_UINT32(alarm_running, GoldfishRTCState), VMSTATE_UINT32(irq_pending, GoldfishRTCState), VMSTATE_UINT32(irq_enabled, GoldfishRTCState), + VMSTATE_UINT32(time_high, GoldfishRTCState), VMSTATE_END_OF_LIST() } }; diff --git a/include/hw/rtc/goldfish_rtc.h b/include/hw/rtc/goldfish_rtc.h index 16f9f9e29d..9bd8924f5f 100644 --- a/include/hw/rtc/goldfish_rtc.h +++ b/include/hw/rtc/goldfish_rtc.h @@ -41,6 +41,7 @@ typedef struct GoldfishRTCState { uint32_t alarm_running; uint32_t irq_pending; uint32_t irq_enabled; + uint32_t time_high; } GoldfishRTCState; #endif -- generated by git-patchbot for /home/xen/git/qemu-xen.git#master
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