Re: [Xen-devel] [PATCH v9 1/5] x86/ioreq server: Release the p2m lock after mmio is handled.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 29.03.17 at 15:39, <dunlapg@xxxxxxxxx> wrote:
> On Tue, Mar 21, 2017 at 2:52 AM, Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
>> 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>
> 
> Who else's ack does this need?  It seems like this is a general
> improvement that can go in without the rest of the series.

I didn't put it in on its own because it didn't really seem useful to
me without the rest of the series.

Jan


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