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SubjectRe: [PATCH] intel-iommu: Don't be too aggressive when clearing one context entry
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Hi Jacob,

> On 30. Aug 2017, at 17:50, Jacob Pan <jacob.jun.pan@linux.intel.com> wrote:
>
> On Mon, 28 Aug 2017 16:16:29 +0200
> Filippo Sironi via iommu <iommu@lists.linux-foundation.org> wrote:
>
>> Previously, we were invalidating context cache and IOTLB globally when
>> clearing one context entry. This is a tad too aggressive.
>> Invalidate the context cache and IOTLB for the interested device only.
>>
>> Signed-off-by: Filippo Sironi <sironi@amazon.de>
>> Cc: David Woodhouse <dwmw@amazon.co.uk>
>> Cc: David Woodhouse <dwmw2@infradead.org>
>> Cc: Joerg Roedel <joro@8bytes.org>
>> Cc: iommu@lists.linux-foundation.org
>> Cc: linux-kernel@vger.kernel.org
>> ---
>> drivers/iommu/intel-iommu.c | 25 ++++++++++++++++++++++---
>> 1 file changed, 22 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
>> index 3e8636f1220e..4bf3e59b0929 100644
>> --- a/drivers/iommu/intel-iommu.c
>> +++ b/drivers/iommu/intel-iommu.c
>> @@ -2351,13 +2351,32 @@ static inline int domain_pfn_mapping(struct
>> dmar_domain *domain, unsigned long i
>> static void domain_context_clear_one(struct intel_iommu *iommu, u8
>> bus, u8 devfn) {
>> + unsigned long flags;
>> + struct context_entry *context;
>> + u16 did_old;
>> +
>> if (!iommu)
>> return;
>>
>> + spin_lock_irqsave(&iommu->lock, flags);
>> + context = iommu_context_addr(iommu, bus, devfn, 0);
>> + if (!context) {
>> + spin_unlock_irqrestore(&iommu->lock, flags);
>> + return;
>> + }
> perhaps check with device_context_mapped()?

Using device_context_mapped() wouldn't simplify the code since it
would just tell me that at the time of check there was a context.
I would still need to lock, get the context, check if the context
is valid, do the work, and unlock.

Modifying device_context_mapped() to return the context isn't
going to work either because it may go away in the meantime since
I wouldn't hold the lock.

>> + did_old = context_domain_id(context);
>> + spin_unlock_irqrestore(&iommu->lock, flags);
>> clear_context_table(iommu, bus, devfn);
>> - iommu->flush.flush_context(iommu, 0, 0, 0,
>> - DMA_CCMD_GLOBAL_INVL);
>> - iommu->flush.flush_iotlb(iommu, 0, 0, 0,
>> DMA_TLB_GLOBAL_FLUSH);
>> + iommu->flush.flush_context(iommu,
>> + did_old,
>> + (((u16)bus) << 8) | devfn,
>> + DMA_CCMD_MASK_NOBIT,
>> + DMA_CCMD_DEVICE_INVL);
>> + iommu->flush.flush_iotlb(iommu,
>> + did_old,
>> + 0,
>> + 0,
>> + DMA_TLB_DSI_FLUSH);
>> }
>>
>> static inline void unlink_domain_info(struct device_domain_info
>> *info)
>
> [Jacob Pan]

Regards,
Filippo


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