Re: [PATCH 08/12] target/i386/mshv: migrate STIMER state

["Doru Blânzeanu" <dblanzeanu@linux.microsoft.com>]

On Fri, Jul 10, 2026 at 12:15:30PM +0200, Magnus Kulke wrote:
> This part of Synic state is retrieved via a mem-aligned page. We declare
> the required space (size reference: rust-vmm/mshv) as a buffer on the VM
> state struct for inclusion in a migration.
> 
> Other than other SynIC features, STIMER doesn't depend on SCONTROL being
> set.
> 
> Signed-off-by: Magnus Kulke <magnuskulke@linux.microsoft.com>
> ---
>  include/system/mshv_int.h   |  2 ++
>  target/i386/cpu.h           |  5 ++++
>  target/i386/machine.c       | 20 +++++++++++++++
>  target/i386/mshv/mshv-cpu.c | 12 +++++++++
>  target/i386/mshv/synic.c    | 51 +++++++++++++++++++++++++++++++++++++
>  5 files changed, 90 insertions(+)
> 
> diff --git a/include/system/mshv_int.h b/include/system/mshv_int.h
> index bc023d3535..063852115e 100644
> --- a/include/system/mshv_int.h
> +++ b/include/system/mshv_int.h
> @@ -144,5 +144,7 @@ int mshv_set_simp(int cpu_fd, const uint8_t *page);
>  int mshv_get_siefp(int cpu_fd, uint8_t *page);
>  int mshv_set_siefp(int cpu_fd, const uint8_t *page);
>  bool mshv_synic_enabled(const CPUState *cpu);
> +int mshv_get_synthetic_timers(int cpu_fd, uint8_t *state);
> +int mshv_set_synthetic_timers(int cpu_fd, const uint8_t *state);
>  
>  #endif
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index 9270ae95d0..6c9e674e81 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -45,6 +45,10 @@
>  #define ELF_MACHINE_UNAME "i686"
>  #endif
>  
> +#ifdef CONFIG_MSHV
> +#define MSHV_STIMERS_STATE_SIZE 200
> +#endif
> +
>  enum {
>      R_EAX = 0,
>      R_ECX = 1,
> @@ -2303,6 +2307,7 @@ typedef struct CPUArchState {
>  #if defined(CONFIG_MSHV)
>      uint8_t hv_simp_page[HV_HYP_PAGE_SIZE];
>      uint8_t hv_siefp_page[HV_HYP_PAGE_SIZE];
> +    uint8_t hv_synthetic_timers_state[MSHV_STIMERS_STATE_SIZE];
>  #endif
>  
>      uint64_t mcg_cap;
> diff --git a/target/i386/machine.c b/target/i386/machine.c
> index 023a397ab8..8d69d7e25e 100644
> --- a/target/i386/machine.c
> +++ b/target/i386/machine.c
> @@ -10,6 +10,7 @@
>  #include "exec/watchpoint.h"
>  #include "system/kvm.h"
>  #include "system/kvm_xen.h"
> +#include "system/mshv.h"
>  #include "system/tcg.h"
>  
>  #include "qemu/error-report.h"
> @@ -952,6 +953,24 @@ static const VMStateDescription vmstate_msr_hyperv_reenlightenment = {
>  };
>  
>  #ifdef CONFIG_MSHV
> +
> +static bool mshv_synthetic_timers_needed(void *opaque)
> +{
> +    /* Always migrate synthetic timers */
> +    return mshv_enabled();
> +}
> +
> +static const VMStateDescription vmstate_mshv_synthetic_timers = {
> +    .name = "cpu/mshv_synthetic_timers",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .needed = mshv_synthetic_timers_needed,
> +    .fields = (const VMStateField[]) {
> +        VMSTATE_BUFFER(env.hv_synthetic_timers_state, X86CPU),
> +        VMSTATE_END_OF_LIST()
> +    }
> +};
> +
>  static bool mshv_synic_vp_state_needed(void *opaque)
>  {
>      X86CPU *cpu = opaque;
> @@ -1941,6 +1960,7 @@ const VMStateDescription vmstate_x86_cpu = {
>  #endif
>  #ifdef CONFIG_MSHV
>          &vmstate_mshv_synic_vp_state,
> +        &vmstate_mshv_synthetic_timers,
>  #endif
>          NULL
>      }
> diff --git a/target/i386/mshv/mshv-cpu.c b/target/i386/mshv/mshv-cpu.c
> index 57244bc667..ce6cfccc0a 100644
> --- a/target/i386/mshv/mshv-cpu.c
> +++ b/target/i386/mshv/mshv-cpu.c
> @@ -118,6 +118,12 @@ static int get_synic_state(CPUState *cpu)
>      int cpu_fd = mshv_vcpufd(cpu);
>      int ret;
>  
> +    ret = mshv_get_synthetic_timers(cpu_fd, env->hv_synthetic_timers_state);
> +    if (ret < 0) {
> +        error_report("failed to get synthetic timers");
> +        return -1;
> +    }
> +
>      /* SIMP/SIEFP can only be read when SynIC is enabled */
>      if (!mshv_synic_enabled(cpu)) {
>          return 0;
> @@ -1420,6 +1426,12 @@ static int set_synic_state(const CPUState *cpu)
>      int cpu_fd = mshv_vcpufd(cpu);
>      int ret;
>  
> +    ret = mshv_set_synthetic_timers(cpu_fd, env->hv_synthetic_timers_state);
> +    if (ret < 0) {
> +        error_report("failed to set synthetic timers state");
> +        return -1;
> +    }
> +
>      /* SIMP/SIEFP can only be written when SynIC is enabled */
>      if (!mshv_synic_enabled(cpu)) {
>          return 0;
> diff --git a/target/i386/mshv/synic.c b/target/i386/mshv/synic.c
> index 8f9fee6ed7..4c629adc3a 100644
> --- a/target/i386/mshv/synic.c
> +++ b/target/i386/mshv/synic.c
> @@ -54,6 +54,57 @@ static int set_vp_state(int cpu_fd, const struct mshv_get_set_vp_state *state)
>      return 0;
>  }
>  
> +int mshv_get_synthetic_timers(int cpu_fd, uint8_t *state)
> +{
> +    int ret;
> +    void *buffer;
> +    struct mshv_get_set_vp_state args = {0};
> +
> +    buffer = qemu_memalign(HV_HYP_PAGE_SIZE, HV_HYP_PAGE_SIZE);
> +    args.buf_ptr = (uint64_t)buffer;
> +    args.buf_sz = HV_HYP_PAGE_SIZE;
> +    args.type = MSHV_VP_STATE_SYNTHETIC_TIMERS;
> +
> +    ret = get_vp_state(cpu_fd, &args);
> +
> +    if (ret < 0) {
> +        qemu_vfree(buffer);
> +        error_report("failed to get synthetic timers");
> +        return -1;
> +    }
> +
> +    memcpy(state, buffer, MSHV_STIMERS_STATE_SIZE);
> +    qemu_vfree(buffer);
> +
> +    return 0;
> +}
> +
> +int mshv_set_synthetic_timers(int cpu_fd, const uint8_t *state)
> +{
> +    int ret;
> +    void *buffer;
> +    struct mshv_get_set_vp_state args = {0};
> +
> +    buffer = qemu_memalign(HV_HYP_PAGE_SIZE, HV_HYP_PAGE_SIZE);
> +    memset(buffer, 0, HV_HYP_PAGE_SIZE);
> +    args.buf_ptr = (uint64_t)buffer;
> +    args.buf_sz = HV_HYP_PAGE_SIZE;
> +    args.type = MSHV_VP_STATE_SYNTHETIC_TIMERS;
> +
> +    assert(state);
> +    memcpy(buffer, state, MSHV_STIMERS_STATE_SIZE);
> +
> +    ret = set_vp_state(cpu_fd, &args);
> +    qemu_vfree(buffer);
> +
> +    if (ret < 0) {
> +        error_report("failed to set synthetic timers");
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
>  int mshv_get_simp(int cpu_fd, uint8_t *page)
>  {
>      int ret;
> -- 
> 2.34.1

Reviewed-by: Doru Blânzeanu <dblanzeanu@linux.microsoft.com>