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

[Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>]

On 3/8/2017 10:06 PM, Paul Durrant wrote:
> > -----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.
Thanks for your remind. Let me try again. This is strange because I had 
commented out supress-cc in my git config.
Please ignore this thread, and sorry for the inconvenience. :-)

Yu
>    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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> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxx
> > https://lists.xen.org/xen-devel

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