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Re: [Qemu-devel] [svt-core] [PATCH] kvmclock: update system_time_msr add
From: |
Roman Kagan |
Subject: |
Re: [Qemu-devel] [svt-core] [PATCH] kvmclock: update system_time_msr address forcibly |
Date: |
Wed, 24 May 2017 18:54:09 +0300 |
User-agent: |
Mutt/1.8.0 (2017-02-23) |
On Wed, May 24, 2017 at 05:07:24PM +0300, Denis Plotnikov wrote:
> Do an update of system_time_msr address every time before reading
> the value of tsc_timestamp from guest's kvmclock page.
>
> It should be done in a forcible manner because there is a situation
> when system_time_msr has been set by kvm but qemu doesn't aware of it.
> This leads to updates of kvmclock_offset without respect of guest's
> kvmclock values.
>
> The situation appears when L2 linux guest runs over L1 linux guest and
> the action inducing system_time_msr update is tpr access reporting.
> Some L1 linux guests turn off processing TPR access and when L0
> gets an L2 exit induced by TPR MSR access it doesn't enter L1 and
> processed it by itself.
> Thus, L1 kvm doesn't know about that TPR access happening and doesn't
> exit to qemu which in turn doesn't set system_time_msr address.
>
> This patch fixes this by making sure it knows the correct address every
> time it is needed.
>
> Signed-off-by: Denis Plotnikov <address@hidden>
> ---
> hw/i386/kvm/clock.c | 32 +++++++++++++++++++++++++++++++-
> 1 file changed, 31 insertions(+), 1 deletion(-)
>
> diff --git a/hw/i386/kvm/clock.c b/hw/i386/kvm/clock.c
> index e713162..035196a 100644
> --- a/hw/i386/kvm/clock.c
> +++ b/hw/i386/kvm/clock.c
> @@ -48,11 +48,38 @@ struct pvclock_vcpu_time_info {
> uint8_t pad[2];
> } __attribute__((__packed__)); /* 32 bytes */
>
> +static void update_all_system_time_msr(void)
> +{
> + CPUState *cpu;
> + CPUX86State *env;
> + struct {
> + struct kvm_msrs info;
> + struct kvm_msr_entry entries[1];
> + } msr_data;
> + int ret;
> +
> + msr_data.info.nmsrs = 1;
> + msr_data.entries[0].index = MSR_KVM_SYSTEM_TIME;
> +
> + CPU_FOREACH(cpu) {
> + ret = kvm_vcpu_ioctl(cpu, KVM_GET_MSRS, &msr_data);
> +
> + if (ret < 0) {
> + fprintf(stderr, "KVM_GET_MSRS failed: %s\n", strerror(ret));
> + abort();
> + }
> +
> + assert(ret == 1);
> + env = cpu->env_ptr;
> + env->system_time_msr = msr_data.entries[0].data;
> + }
> +}
> +
> static uint64_t kvmclock_current_nsec(KVMClockState *s)
> {
> CPUState *cpu = first_cpu;
> CPUX86State *env = cpu->env_ptr;
> - hwaddr kvmclock_struct_pa = env->system_time_msr & ~1ULL;
> + hwaddr kvmclock_struct_pa;
> uint64_t migration_tsc = env->tsc;
> struct pvclock_vcpu_time_info time;
> uint64_t delta;
> @@ -60,6 +87,9 @@ static uint64_t kvmclock_current_nsec(KVMClockState *s)
> uint64_t nsec_hi;
> uint64_t nsec;
>
> + update_all_system_time_msr();
I'd rather just cpu_synchronize_state(cpu) here.
> + kvmclock_struct_pa = env->system_time_msr & ~1ULL;
> +
> if (!(env->system_time_msr & 1ULL)) {
> /* KVM clock not active */
> return 0;
Roman.