Re: [PATCH v5 2/6] vpci: fix deferral of long operations

["Jan Beulich" <JBeulich@suse.com>]

>>> On 20.11.18 at 17:01, <roger.pau@citrix.com> wrote:
> Current logic to handle long running operations is flawed because it
> doesn't prevent the guest vcpu from running. Fix this by raising a
> scheduler softirq when preemption is required, so that the do_softirq
> call in the guest entry path performs a rescheduling. Also move the
> call to vpci_process_pending into handle_hvm_io_completion, together
> with the IOREQ code that handles pending IO instructions.
> 
> Note that a scheduler softirq is also raised when the long running
> operation is queued in order to prevent the guest vcpu from resuming
> execution.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> ---
> Cc: Paul Durrant <paul.durrant@citrix.com>
> Cc: Jan Beulich <jbeulich@suse.com>
> Cc: Andrew Cooper <andrew.cooper3@citrix.com>
> Cc: Wei Liu <wei.liu2@citrix.com>
> Cc: George Dunlap <George.Dunlap@eu.citrix.com>
> Cc: Ian Jackson <ian.jackson@eu.citrix.com>
> Cc: Julien Grall <julien.grall@arm.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Cc: Stefano Stabellini <sstabellini@kernel.org>
> Cc: Tim Deegan <tim@xen.org>
> ---
> Changes since v4:
>  - Add a comment to clarify defer_map raising a scheduler softirq.
>  - Reword commit message.
>  - Raise the scheduler softirq in handle_hvm_io_completion rather than
>    vpci_process_pending.
> 
> Changes since v3:
>  - Don't use a tasklet.
> ---
>  xen/arch/x86/hvm/ioreq.c  | 9 ++++++---

Paul - I'll take the liberty and reinstate your v4 R-b for v5.

Jan

>  xen/drivers/vpci/header.c | 5 +++++
>  2 files changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/ioreq.c b/xen/arch/x86/hvm/ioreq.c
> index a56d634f31..71f23227e6 100644
> --- a/xen/arch/x86/hvm/ioreq.c
> +++ b/xen/arch/x86/hvm/ioreq.c
> @@ -85,9 +85,6 @@ bool hvm_io_pending(struct vcpu *v)
>      struct hvm_ioreq_server *s;
>      unsigned int id;
>  
> -    if ( has_vpci(d) && vpci_process_pending(v) )
> -        return true;
> -
>      FOR_EACH_IOREQ_SERVER(d, id, s)
>      {
>          struct hvm_ioreq_vcpu *sv;
> @@ -186,6 +183,12 @@ bool handle_hvm_io_completion(struct vcpu *v)
>      enum hvm_io_completion io_completion;
>      unsigned int id;
>  
> +    if ( has_vpci(d) && vpci_process_pending(v) )
> +    {
> +        raise_softirq(SCHEDULE_SOFTIRQ);
> +        return false;
> +    }
> +
>      FOR_EACH_IOREQ_SERVER(d, id, s)
>      {
>          struct hvm_ioreq_vcpu *sv;
> diff --git a/xen/drivers/vpci/header.c b/xen/drivers/vpci/header.c
> index 39dffb21fb..c9bdc2ced3 100644
> --- a/xen/drivers/vpci/header.c
> +++ b/xen/drivers/vpci/header.c
> @@ -184,6 +184,11 @@ static void defer_map(struct domain *d, struct pci_dev 
> *pdev,
>      curr->vpci.mem = mem;
>      curr->vpci.cmd = cmd;
>      curr->vpci.rom_only = rom_only;
> +    /*
> +     * Raise a scheduler softirq in order to prevent the guest from 
> resuming
> +     * execution with pending mapping operations.
> +     */
> +    raise_softirq(SCHEDULE_SOFTIRQ);
>  }
>  
>  static int modify_bars(const struct pci_dev *pdev, uint16_t cmd, bool 
> rom_only)
> -- 
> 2.19.1




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