Re: [PATCH v3 11/11] xen/arm: Process pending vPCI map/unmap operations

[Jan Beulich <jbeulich@xxxxxxxx>]

On 30.09.2021 09:13, Oleksandr Andrushchenko wrote:
> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> 
> vPCI may map and unmap PCI device memory (BARs) being passed through which
> may take a lot of time. For this those operations may be deferred to be
> performed later, so that they can be safely preempted.
> 
> Currently this deferred processing is happening in common IOREQ code
> which doesn't seem to be the right place for x86 and is even more
> doubtful because IOREQ may not be enabled for Arm at all.
> So, for Arm the pending vPCI work may have no chance to be executed
> if the processing is left as is in the common IOREQ code only.
> For that reason make vPCI processing happen in arch specific code.
> 
> Please be aware that there are a few outstanding TODOs affecting this
> code path, see xen/drivers/vpci/header.c:map_range and
> xen/drivers/vpci/header.c:vpci_process_pending.
> 
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> 
> ---
> Since v2:
>  - update commit message with more insight on x86, IOREQ and Arm
>  - restored order of invocation for IOREQ and vPCI processing (Jan)
> Since v1:
>  - Moved the check for pending vpci work from the common IOREQ code
>    to hvm_do_resume on x86
>  - Re-worked the code for Arm to ensure we don't miss pending vPCI work
> ---
>  xen/arch/arm/traps.c   | 13 +++++++++++++
>  xen/arch/x86/hvm/hvm.c |  6 ++++++

This x86 change
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

>  xen/common/ioreq.c     |  9 ---------

Already on v2 I did indicate that you need to Cc Paul to get an ack for
this part of the change.

> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -546,6 +546,12 @@ void hvm_do_resume(struct vcpu *v)
>  
>      pt_restore_timer(v);
>  
> +    if ( has_vpci(v->domain) && vpci_process_pending(v) )
> +    {
> +        raise_softirq(SCHEDULE_SOFTIRQ);
> +        return;
> +    }
> +
>      if ( !vcpu_ioreq_handle_completion(v) )
>          return;

Seeing this movement I'm now wondering whether we shouldn't take the
opportunity and move this further up. I notice that besides Paul you
also failed to Cc the other x86 maintainers, whom I'm now adding.

Jan

> --- a/xen/common/ioreq.c
> +++ b/xen/common/ioreq.c
> @@ -25,9 +25,7 @@
>  #include <xen/lib.h>
>  #include <xen/paging.h>
>  #include <xen/sched.h>
> -#include <xen/softirq.h>
>  #include <xen/trace.h>
> -#include <xen/vpci.h>
>  
>  #include <asm/guest_atomics.h>
>  #include <asm/ioreq.h>
> @@ -212,19 +210,12 @@ static bool wait_for_io(struct ioreq_vcpu *sv, ioreq_t 
> *p)
>  
>  bool vcpu_ioreq_handle_completion(struct vcpu *v)
>  {
> -    struct domain *d = v->domain;
>      struct vcpu_io *vio = &v->io;
>      struct ioreq_server *s;
>      struct ioreq_vcpu *sv;
>      enum vio_completion completion;
>      bool res = true;
>  
> -    if ( has_vpci(d) && vpci_process_pending(v) )
> -    {
> -        raise_softirq(SCHEDULE_SOFTIRQ);
> -        return false;
> -    }
> -
>      while ( (sv = get_pending_vcpu(v, &s)) != NULL )
>          if ( !wait_for_io(sv, get_ioreq(s, v)) )
>              return false;
>