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Re: [PATCH] target/i386: properly reset TSC on reset
From: |
Marcelo Tosatti |
Subject: |
Re: [PATCH] target/i386: properly reset TSC on reset |
Date: |
Mon, 9 May 2022 11:54:00 -0300 |
On Thu, Mar 24, 2022 at 06:31:36PM +0100, Paolo Bonzini wrote:
> Some versions of Windows hang on reboot if their TSC value is greater
> than 2^54. The calibration of the Hyper-V reference time overflows
> and fails; as a result the processors' clock sources are out of sync.
>
> The issue is that the TSC _should_ be reset to 0 on CPU reset and
> QEMU tries to do that. However, KVM special cases writing 0 to the
> TSC and thinks that QEMU is trying to hot-plug a CPU, which is
> correct the first time through but not later. Thwart this valiant
> effort and reset the TSC to 1 instead, but only if the CPU has been
> run once.
>
> For this to work, env->tsc has to be moved to the part of CPUArchState
> that is not zeroed at the beginning of x86_cpu_reset.
>
> Reported-by: Vadim Rozenfeld <vrozenfe@redhat.com>
> Supersedes: <20220324082346.72180-1-pbonzini@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Paolo,
Won't this disable the logic to sync TSCs, making it possible
for TSC of SMP guests to go out of sync? (And remember the logic
to sync TSCs from within a guest is fragile, in case of VCPU overload
for example).
> ---
> target/i386/cpu.c | 13 +++++++++++++
> target/i386/cpu.h | 2 +-
> 2 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index ec3b50bf6e..cb6b5467d0 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -5931,6 +5931,19 @@ static void x86_cpu_reset(DeviceState *dev)
> env->xstate_bv = 0;
>
> env->pat = 0x0007040600070406ULL;
> +
> + if (kvm_enabled()) {
> + /*
> + * KVM handles TSC = 0 specially and thinks we are hot-plugging
> + * a new CPU, use 1 instead to force a reset.
> + */
> + if (env->tsc != 0) {
> + env->tsc = 1;
> + }
> + } else {
> + env->tsc = 0;
> + }
> +
> env->msr_ia32_misc_enable = MSR_IA32_MISC_ENABLE_DEFAULT;
> if (env->features[FEAT_1_ECX] & CPUID_EXT_MONITOR) {
> env->msr_ia32_misc_enable |= MSR_IA32_MISC_ENABLE_MWAIT;
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index e31e6bd8b8..982c532353 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -1554,7 +1554,6 @@ typedef struct CPUArchState {
> target_ulong kernelgsbase;
> #endif
>
> - uint64_t tsc;
> uint64_t tsc_adjust;
> uint64_t tsc_deadline;
> uint64_t tsc_aux;
> @@ -1708,6 +1707,7 @@ typedef struct CPUArchState {
> int64_t tsc_khz;
> int64_t user_tsc_khz; /* for sanity check only */
> uint64_t apic_bus_freq;
> + uint64_t tsc;
> #if defined(CONFIG_KVM) || defined(CONFIG_HVF)
> void *xsave_buf;
> uint32_t xsave_buf_len;
> --
> 2.35.1
>
>
>
- Re: [PATCH] target/i386: properly reset TSC on reset,
Marcelo Tosatti <=