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

[Yu Zhang <yu.c.zhang@linux.intel.com>]

On 3/8/2017 10:06 PM, Paul Durrant wrote:
>> -----Original Message-----
>> From: Xen-devel [mailto:xen-devel-bounces@lists.xen.org] On Behalf Of Yu
>> Zhang
>> Sent: 08 March 2017 13:32
>> To: xen-devel@lists.xen.org
>> Cc: zhiyuan.lv@intel.com
>> 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@linux.intel.com>
>> Reviewed-by: Jan Beulich <jbeulich@suse.com>
>> ---
>> Cc: Paul Durrant <paul.durrant@citrix.com>
>> Cc: Jan Beulich <jbeulich@suse.com>
>> Cc: Andrew Cooper <andrew.cooper3@citrix.com>
> 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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>> https://lists.xen.org/xen-devel


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