Re: [Xen-devel] [PATCH v7 1/5] x86/ioreq server: Release the p2m lock after mmio is handled.

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Xen-devel [mailto:xen-devel-bounces@xxxxxxxxxxxxx] On Behalf Of Yu
> Zhang
> Sent: 08 March 2017 13:32
> To: xen-devel@xxxxxxxxxxxxx
> Cc: zhiyuan.lv@xxxxxxxxx
> Subject: [Xen-devel] [PATCH v7 1/5] x86/ioreq server: Release the p2m lock
> after mmio is handled.
> 
> Routine hvmemul_do_io() may need to peek the p2m type of a gfn to
> select the ioreq server. For example, operations on gfns with
> p2m_ioreq_server type will be delivered to a corresponding ioreq
> server, and this requires that the p2m type not be switched back
> to p2m_ram_rw during the emulation process. To avoid this race
> condition, we delay the release of p2m lock in
> hvm_hap_nested_page_fault()
> until mmio is handled.
> 
> Note: previously in hvm_hap_nested_page_fault(), put_gfn() was moved
> before the handling of mmio, due to a deadlock risk between the p2m
> lock and the event lock(in commit 77b8dfe). Later, a per-event channel
> lock was introduced in commit de6acb7, to send events. So we do not
> need to worry about the deadlock issue.
> 
> Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> Cc: Paul Durrant <paul.durrant@xxxxxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Your cc-s seem to have been dropped by your mailer (or at least I can't see 
them in the mail header). You may want to send these again so that relevant 
folks actually get cc-ed.

  Paul

> ---
>  xen/arch/x86/hvm/hvm.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index ccfae4f..a9db7f7 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -1870,18 +1870,14 @@ int hvm_hap_nested_page_fault(paddr_t gpa,
> unsigned long gla,
>           (npfec.write_access &&
>            (p2m_is_discard_write(p2mt) || (p2mt == p2m_ioreq_server))) )
>      {
> -        __put_gfn(p2m, gfn);
> -        if ( ap2m_active )
> -            __put_gfn(hostp2m, gfn);
> -
>          rc = 0;
>          if ( unlikely(is_pvh_domain(currd)) )
> -            goto out;
> +            goto out_put_gfn;
> 
>          if ( !handle_mmio_with_translation(gla, gpa >> PAGE_SHIFT, npfec) )
>              hvm_inject_hw_exception(TRAP_gp_fault, 0);
>          rc = 1;
> -        goto out;
> +        goto out_put_gfn;
>      }
> 
>      /* Check if the page has been paged out */
> --
> 1.9.1
> 
> 
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