Re: [Xen-devel] [PATCH] passthrough/pci: properly qualify the mem_sharing_enabled check...

[Jan Beulich <JBeulich@xxxxxxxx>]

On 03.07.2019 15:25, Paul Durrant wrote:
>> -----Original Message-----
>> From: Jan Beulich <JBeulich@xxxxxxxx>
>> Sent: 03 July 2019 14:20
>> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
>> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Roger Pau Monne 
>> <roger.pau@xxxxxxxxxx>; George Dunlap
>> <George.Dunlap@xxxxxxxxxx>; Tamas K Lengyel <tamas@xxxxxxxxxxxxx>; WeiLiu 
>> <wl@xxxxxxx>
>> Subject: Re: [PATCH] passthrough/pci: properly qualify the 
>> mem_sharing_enabled check...
>>
>> On 01.07.2019 15:17, Paul Durrant wrote:
>>> --- a/xen/drivers/passthrough/pci.c
>>> +++ b/xen/drivers/passthrough/pci.c
>>> @@ -1450,7 +1450,7 @@ static int assign_device(struct domain *d, u16 seg, 
>>> u8 bus, u8 devfn, u32
>> flag)
>>>
>>>        /* Prevent device assign if mem paging or mem sharing have been
>>>         * enabled for this domain */
>>> -    if ( unlikely(d->arch.hvm.mem_sharing_enabled ||
>>> +    if ( unlikely(mem_sharing_enabled(d) ||
>>>                      vm_event_check_ring(d->vm_event_paging) ||
>>>                      p2m_get_hostp2m(d)->global_logdirty) )
>>>            return -EXDEV;
>>
>> This change is redundant with the more extensive one by
>> "x86/HVM: p2m_ram_ro is incompatible with device pass-through",
>> of which I've sent v2 earlier today, and v1 of which has been
>> pending for quite some time without having heard back from
>> other than you.
> 
> Agreed, but I still think it's a good idea to move the
> mem_sharing_enabled() macro into domain.h, so maybe incorporate
> that into your patch?

Hmm, that would actually have been a question of mine if I hadn't
recognized the redundancy: Why domain.h rather than mem_sharing.h?
Furthermore I'd rather not use it here anyway, to avoid two
consecutive is_hvm_*() checks (which have become slightly more
expensive with the LFENCE addition).

Jan
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