Re: [Qemu-devel] [PATCH 1/2] spapr: Fix stale HTAB during live migration (KVM)

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 11/05/2014 05:17 PM, Samuel Mendoza-Jonas wrote:
> If a guest reboots during a running migration, changes to the
> hash page table are not necessarily updated on the destination.
> Opening a new file descriptor to the HTAB forces the migration
> handler to resend the entire table.
> 
> Signed-off-by: Samuel Mendoza-Jonas <sam.mj@au1.ibm.com>
> ---
>  hw/ppc/spapr.c         | 47 +++++++++++++++++++++++++++++++++++++++++++++++
>  include/hw/ppc/spapr.h |  2 ++
>  2 files changed, 49 insertions(+)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 0a2bfe6..1610c28 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -833,6 +833,13 @@ static void spapr_reset_htab(sPAPREnvironment *spapr)
>          /* Kernel handles htab, we don't need to allocate one */
>          spapr->htab_shift = shift;
>          kvmppc_kern_htab = true;
> +
> +        /* Tell readers to update their file descriptor */
> +        pthread_mutex_lock(&spapr->htab_mutex);
> +        if (spapr->htab_fd > 0) {

s/>/>=/
htab_fd == 0 is correct.


> +            spapr->htab_fd_stale = true;
> +        }
> +        pthread_mutex_unlock(&spapr->htab_mutex);
>      } else {
>          if (!spapr->htab) {
>              /* Allocate an htab if we don't yet have one */
> @@ -850,6 +857,31 @@ static void spapr_reset_htab(sPAPREnvironment *spapr)
>      }
>  }
>  
> +/* A guest reset will cause spapr->htab_fd to become stale if being used.

Multiline comment starts with /* and \n.


> + * Reopen the file descriptor to make sure the whole HTAB is properly read.
> + */
> +static int spapr_check_htab_fd(sPAPREnvironment *spapr)
> +{
> +    int rc = 0;
> +
> +    pthread_mutex_lock(&spapr->htab_mutex);
> +
> +    if (spapr->htab_fd_stale) {
> +        close(spapr->htab_fd);
> +        spapr->htab_fd = kvmppc_get_htab_fd(false);
> +        if (spapr->htab_fd < 0) {
> +            error_report("Unable to open fd for reading hash table from KVM: "
> +                    "%s", strerror(errno));
> +            rc = -1;
> +        }
> +        spapr->htab_fd_stale = false;
> +    }
> +
> +    pthread_mutex_unlock(&spapr->htab_mutex);
> +    return rc;
> +}
> +
> +

2 empty lines, should be one.


>  static void ppc_spapr_reset(void)
>  {
>      PowerPCCPU *first_ppc_cpu;
> @@ -984,7 +1016,10 @@ static int htab_save_setup(QEMUFile *f, void *opaque)
>      } else {
>          assert(kvm_enabled());
>  
> +        pthread_mutex_lock(&spapr->htab_mutex);
>          spapr->htab_fd = kvmppc_get_htab_fd(false);
> +        spapr->htab_fd_stale = false;
> +        pthread_mutex_unlock(&spapr->htab_mutex);
>          if (spapr->htab_fd < 0) {
>              fprintf(stderr, "Unable to open fd for reading hash table from KVM: %s\n",
>                      strerror(errno));
> @@ -1137,6 +1172,11 @@ static int htab_save_iterate(QEMUFile *f, void *opaque)
>      if (!spapr->htab) {
>          assert(kvm_enabled());
>  
> +        rc = spapr_check_htab_fd(spapr);
> +        if (rc < 0) {
> +            return rc;
> +        }
> +
>          rc = kvmppc_save_htab(f, spapr->htab_fd,
>                                MAX_KVM_BUF_SIZE, MAX_ITERATION_NS);
>          if (rc < 0) {
> @@ -1168,6 +1208,11 @@ static int htab_save_complete(QEMUFile *f, void *opaque)
>  
>          assert(kvm_enabled());
>  
> +        rc = spapr_check_htab_fd(spapr);
> +        if (rc < 0) {
> +            return rc;
> +        }
> +
>          rc = kvmppc_save_htab(f, spapr->htab_fd, MAX_KVM_BUF_SIZE, -1);
>          if (rc < 0) {
>              return rc;
> @@ -1355,6 +1400,8 @@ static void ppc_spapr_init(MachineState *machine)
>          spapr->htab_shift++;
>      }
>  
> +    pthread_mutex_init(&spapr->htab_mutex, NULL);
> +
>      /* Set up Interrupt Controller before we create the VCPUs */
>      spapr->icp = xics_system_init(smp_cpus * kvmppc_smt_threads() / smp_threads,
>                                    XICS_IRQS);
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index 749daf4..5e29bec 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -37,6 +37,8 @@ typedef struct sPAPREnvironment {
>      int htab_save_index;
>      bool htab_first_pass;
>      int htab_fd;
> +    bool htab_fd_stale;
> +    pthread_mutex_t htab_mutex;
>  } sPAPREnvironment;
>  
>  #define H_SUCCESS         0
> 


-- 
Alexey