Re: [PATCH v2 2/2] IOREQ: refine when to send mapcache invalidation request

[Jan Beulich <jbeulich@suse.com>]

On 02.02.2021 16:14, Jan Beulich wrote:
> XENMEM_decrease_reservation isn't the only means by which pages can get
> removed from a guest, yet all removals ought to be signaled to qemu. Put
> setting of the flag into the central p2m_remove_page() underlying all
> respective hypercalls as well as a few similar places, mainly in PoD
> code.
> 
> Additionally there's no point sending the request for the local domain
> when the domain acted upon is a different one. The latter domain's ioreq
> server mapcaches need invalidating. We assume that domain to be paused
> at the point the operation takes place, so sending the request in this
> case happens from the hvm_do_resume() path, which as one of its first
> steps calls handle_hvm_io_completion().
> 
> Even without the remote operation aspect a single domain-wide flag
> doesn't do: Guests may e.g. decrease-reservation on multiple vCPU-s in
> parallel. Each of them needs to issue an invalidation request in due
> course, in particular because exiting to guest context should not happen
> before the request was actually seen by (all) the emulator(s).
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> ---
> v2: Preemption related adjustment split off. Make flag per-vCPU. More
>     places to set the flag. Also handle acting on a remote domain.
>     Re-base.

Can I get an Arm side ack (or otherwise) please?

Thanks, Jan

> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -759,10 +759,9 @@ static void p2m_free_entry(struct p2m_do
>           * has failed (error case).
>           * So, at worst, the spurious mapcache invalidation might be sent.
>           */
> -        if ( (p2m->domain == current->domain) &&
> -              domain_has_ioreq_server(p2m->domain) &&
> -              p2m_is_ram(entry.p2m.type) )
> -            p2m->domain->mapcache_invalidate = true;
> +        if ( p2m_is_ram(entry.p2m.type) &&
> +             domain_has_ioreq_server(p2m->domain) )
> +            ioreq_request_mapcache_invalidate(p2m->domain);
>  #endif
>  
>          p2m->stats.mappings[level]--;
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -1509,8 +1509,8 @@ static void do_trap_hypercall(struct cpu
>       * Note that sending the invalidation request causes the vCPU to block
>       * until all the IOREQ servers have acknowledged the invalidation.
>       */
> -    if ( unlikely(curr->domain->mapcache_invalidate) &&
> -         test_and_clear_bool(curr->domain->mapcache_invalidate) )
> +    if ( unlikely(curr->mapcache_invalidate) &&
> +         test_and_clear_bool(curr->mapcache_invalidate) )
>          ioreq_signal_mapcache_invalidate();
>  #endif
>  }
> --- a/xen/arch/x86/hvm/hypercall.c
> +++ b/xen/arch/x86/hvm/hypercall.c
> @@ -32,7 +32,6 @@
>  
>  static long hvm_memory_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
>  {
> -    const struct vcpu *curr = current;
>      long rc;
>  
>      switch ( cmd & MEMOP_CMD_MASK )
> @@ -42,14 +41,11 @@ static long hvm_memory_op(int cmd, XEN_G
>          return -ENOSYS;
>      }
>  
> -    if ( !curr->hcall_compat )
> +    if ( !current->hcall_compat )
>          rc = do_memory_op(cmd, arg);
>      else
>          rc = compat_memory_op(cmd, arg);
>  
> -    if ( (cmd & MEMOP_CMD_MASK) == XENMEM_decrease_reservation )
> -        curr->domain->mapcache_invalidate = true;
> -
>      return rc;
>  }
>  
> @@ -327,9 +323,11 @@ int hvm_hypercall(struct cpu_user_regs *
>  
>      HVM_DBG_LOG(DBG_LEVEL_HCALL, "hcall%lu -> %lx", eax, regs->rax);
>  
> -    if ( unlikely(currd->mapcache_invalidate) &&
> -         test_and_clear_bool(currd->mapcache_invalidate) )
> +    if ( unlikely(curr->mapcache_invalidate) )
> +    {
> +        curr->mapcache_invalidate = false;
>          ioreq_signal_mapcache_invalidate();
> +    }
>  
>      return curr->hcall_preempted ? HVM_HCALL_preempted : HVM_HCALL_completed;
>  }
> --- a/xen/arch/x86/mm/p2m.c
> +++ b/xen/arch/x86/mm/p2m.c
> @@ -28,6 +28,7 @@
>  #include <xen/vm_event.h>
>  #include <xen/event.h>
>  #include <xen/grant_table.h>
> +#include <xen/ioreq.h>
>  #include <xen/param.h>
>  #include <public/vm_event.h>
>  #include <asm/domain.h>
> @@ -815,6 +816,8 @@ p2m_remove_page(struct p2m_domain *p2m,
>          }
>      }
>  
> +    ioreq_request_mapcache_invalidate(p2m->domain);
> +
>      return p2m_set_entry(p2m, gfn, INVALID_MFN, page_order, p2m_invalid,
>                           p2m->default_access);
>  }
> @@ -1301,6 +1304,8 @@ static int set_typed_p2m_entry(struct do
>              ASSERT(mfn_valid(mfn_add(omfn, i)));
>              set_gpfn_from_mfn(mfn_x(omfn) + i, INVALID_M2P_ENTRY);
>          }
> +
> +        ioreq_request_mapcache_invalidate(d);
>      }
>  
>      P2M_DEBUG("set %d %lx %lx\n", gfn_p2mt, gfn_l, mfn_x(mfn));
> --- a/xen/arch/x86/mm/p2m-pod.c
> +++ b/xen/arch/x86/mm/p2m-pod.c
> @@ -20,6 +20,7 @@
>   */
>  
>  #include <xen/event.h>
> +#include <xen/ioreq.h>
>  #include <xen/mm.h>
>  #include <xen/sched.h>
>  #include <xen/trace.h>
> @@ -647,6 +648,8 @@ p2m_pod_decrease_reservation(struct doma
>                  set_gpfn_from_mfn(mfn_x(mfn), INVALID_M2P_ENTRY);
>              p2m_pod_cache_add(p2m, page, cur_order);
>  
> +            ioreq_request_mapcache_invalidate(d);
> +
>              steal_for_cache =  ( p2m->pod.entry_count > p2m->pod.count );
>  
>              ram -= n;
> @@ -835,6 +838,8 @@ p2m_pod_zero_check_superpage(struct p2m_
>      p2m_pod_cache_add(p2m, mfn_to_page(mfn0), PAGE_ORDER_2M);
>      p2m->pod.entry_count += SUPERPAGE_PAGES;
>  
> +    ioreq_request_mapcache_invalidate(d);
> +
>      ret = SUPERPAGE_PAGES;
>  
>  out_reset:
> @@ -997,6 +1002,8 @@ p2m_pod_zero_check(struct p2m_domain *p2
>              /* Add to cache, and account for the new p2m PoD entry */
>              p2m_pod_cache_add(p2m, mfn_to_page(mfns[i]), PAGE_ORDER_4K);
>              p2m->pod.entry_count++;
> +
> +            ioreq_request_mapcache_invalidate(d);
>          }
>      }
>  
> @@ -1315,6 +1322,8 @@ guest_physmap_mark_populate_on_demand(st
>          p2m->pod.entry_count -= pod_count;
>          BUG_ON(p2m->pod.entry_count < 0);
>          pod_unlock(p2m);
> +
> +        ioreq_request_mapcache_invalidate(d);
>      }
>  
>  out:
> --- a/xen/common/ioreq.c
> +++ b/xen/common/ioreq.c
> @@ -35,6 +35,17 @@
>  #include <public/hvm/ioreq.h>
>  #include <public/hvm/params.h>
>  
> +void ioreq_request_mapcache_invalidate(const struct domain *d)
> +{
> +    struct vcpu *v = current;
> +
> +    if ( d == v->domain )
> +        v->mapcache_invalidate = true;
> +    else if ( d->creation_finished )
> +        for_each_vcpu ( d, v )
> +            v->mapcache_invalidate = true;
> +}
> +
>  /* Ask ioemu mapcache to invalidate mappings. */
>  void ioreq_signal_mapcache_invalidate(void)
>  {
> @@ -206,6 +217,7 @@ bool vcpu_ioreq_handle_completion(struct
>      struct ioreq_server *s;
>      struct ioreq_vcpu *sv;
>      enum vio_completion completion;
> +    bool res = true;
>  
>      if ( has_vpci(d) && vpci_process_pending(v) )
>      {
> @@ -232,17 +244,27 @@ bool vcpu_ioreq_handle_completion(struct
>          break;
>  
>      case VIO_mmio_completion:
> -        return arch_ioreq_complete_mmio();
> +        res = arch_ioreq_complete_mmio();
> +        break;
>  
>      case VIO_pio_completion:
> -        return handle_pio(vio->req.addr, vio->req.size,
> -                          vio->req.dir);
> +        res = handle_pio(vio->req.addr, vio->req.size,
> +                         vio->req.dir);
> +        break;
>  
>      default:
> -        return arch_vcpu_ioreq_completion(completion);
> +        res = arch_vcpu_ioreq_completion(completion);
> +        break;
>      }
>  
> -    return true;
> +    if ( res && unlikely(v->mapcache_invalidate) )
> +    {
> +        v->mapcache_invalidate = false;
> +        ioreq_signal_mapcache_invalidate();
> +        res = false;
> +    }
> +
> +    return res;
>  }
>  
>  static int ioreq_server_alloc_mfn(struct ioreq_server *s, bool buf)
> --- a/xen/include/xen/ioreq.h
> +++ b/xen/include/xen/ioreq.h
> @@ -103,6 +103,7 @@ struct ioreq_server *ioreq_server_select
>  int ioreq_send(struct ioreq_server *s, ioreq_t *proto_p,
>                 bool buffered);
>  unsigned int ioreq_broadcast(ioreq_t *p, bool buffered);
> +void ioreq_request_mapcache_invalidate(const struct domain *d);
>  void ioreq_signal_mapcache_invalidate(void);
>  
>  void ioreq_domain_init(struct domain *d);
> --- a/xen/include/xen/sched.h
> +++ b/xen/include/xen/sched.h
> @@ -225,6 +225,14 @@ struct vcpu
>      bool             hcall_compat;
>  #endif
>  
> +#ifdef CONFIG_IOREQ_SERVER
> +    /*
> +     * Indicates that mapcache invalidation request should be sent to
> +     * the device emulator.
> +     */
> +    bool             mapcache_invalidate;
> +#endif
> +
>      /* The CPU, if any, which is holding onto this VCPU's state. */
>  #define VCPU_CPU_CLEAN (~0u)
>      unsigned int     dirty_cpu;
> @@ -444,11 +452,6 @@ struct domain
>       * unpaused for the first time by the systemcontroller.
>       */
>      bool             creation_finished;
> -    /*
> -     * Indicates that mapcache invalidation request should be sent to
> -     * the device emulator.
> -     */
> -    bool             mapcache_invalidate;
>  
>      /* Which guest this guest has privileges on */
>      struct domain   *target;
>