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Re: [PATCH 3/4] VT-d: replace flush_all_cache()
- To: Andrew Cooper <amc96@xxxxxxxx>, Kevin Tian <kevin.tian@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 2 Dec 2021 09:47:32 +0100
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- Cc: Paul Durrant <paul@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 02 Dec 2021 08:47:48 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 01.12.2021 14:02, Andrew Cooper wrote:
> On 01/12/2021 09:41, Jan Beulich wrote:
>> --- a/xen/drivers/passthrough/vtd/iommu.c
>> +++ b/xen/drivers/passthrough/vtd/iommu.c
>> @@ -591,7 +591,8 @@ static int __must_check iommu_flush_all(
>> bool_t flush_dev_iotlb;
>> int rc = 0;
>>
>> - flush_all_cache();
>> + flush_local(FLUSH_CACHE);
>
> While I agree that the conversion is an improvement, the logic still
> looks totally bogus.
>
> I can believe that it might have been a stopgap to fix problems before
> we identified the need for sync_cache() for non-coherent IOMMUs, but
> there's no need I can spot for any WBINVDs on any of these paths.
>
> I'm fairly sure this should just be dropped, and Xen will get faster as
> a result.
Kevin, thoughts? I have to admit I'm hesitant to remove such code, when
there's no clear indication why it's there. I'm also not sure how much
of a win the dropping would be, considering the places where this
function gets called from.
Jan
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