linux-kernel - Re: [PATCH v2 0/4] iommu/amd: Enable page-selective flushes

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Date:   Fri, 4 Jun 2021 19:53:31 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Nadav Amit <nadav.amit@...il.com>, Joerg Roedel <joro@...tes.org>
Cc:     Will Deacon <will@...nel.org>, Jiajun Cao <caojiajun@...are.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/4] iommu/amd: Enable page-selective flushes

On 2021-06-04 18:10, Nadav Amit wrote:
> 
> 
>> On Jun 4, 2021, at 8:38 AM, Joerg Roedel <joro@...tes.org> wrote:
>>
>> Hi Nadav,
>>
>> [Adding Robin]
>>
>> On Mon, May 24, 2021 at 03:41:55PM -0700, Nadav Amit wrote:
>>> Nadav Amit (4):
>>>   iommu/amd: Fix wrong parentheses on page-specific invalidations
>>
>> This patch is already upstream in v5.13-rc4. Please rebase to that
>> version.
> 
> I guess it would be rc5 by the time I send it.
> 
>>
>>>   iommu/amd: Selective flush on unmap
>>>   iommu/amd: Do not sync on page size changes
>>>   iommu/amd: Do not use flush-queue when NpCache is on
>>
>> And I think there have been objections from Robin Murphy on Patch 3,
>> have those been worked out?
> 
> I am still waiting for Robin’s feedback on my proposed changes. If he does not respond soon, I will drop this patch for now.

Apologies, it feels like I've spent most of this week fighting fires,
and a great deal of email got skimmed and mentally filed under "nothing
so wrong that I need to respond immediately"...

FWIW I would have written the simpler patch below, but beyond that I
think it might start descending into bikeshedding - if you still prefer
your more comprehensive refactoring, or something in between, then don't
let my personal preference in style/complexity trade-offs stand in the
way of getting a useful functional change into the AMD driver. Whichever
way, though, I *am* now sold on the idea of having some kerneldoc to
clarify these things.

Thanks,
Robin.

----->8-----
From: Robin Murphy <robin.murphy@....com>
Subject: [PATCH] iommu: Improve iommu_iotlb_gather helpers

The Mediatek driver is not the only one which might want a basic
address-based gathering behaviour, so although it's arguably simple
enough to open-code, let's factor it out for the sake of cleanliness.
Let's also take this opportunity to document the intent of these
helpers for clarity.

Signed-off-by: Robin Murphy <robin.murphy@....com>
---
  drivers/iommu/mtk_iommu.c |  6 +-----
  include/linux/iommu.h     | 32 ++++++++++++++++++++++++++++++++
  2 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
index e06b8a0e2b56..cd457487ce81 100644
--- a/drivers/iommu/mtk_iommu.c
+++ b/drivers/iommu/mtk_iommu.c
@@ -521,12 +521,8 @@ static size_t mtk_iommu_unmap(struct iommu_domain *domain,
  			      struct iommu_iotlb_gather *gather)
  {
  	struct mtk_iommu_domain *dom = to_mtk_domain(domain);
-	unsigned long end = iova + size - 1;
  
-	if (gather->start > iova)
-		gather->start = iova;
-	if (gather->end < end)
-		gather->end = end;
+	iommu_iotlb_gather_add_range(gather, iova, size);
  	return dom->iop->unmap(dom->iop, iova, size, gather);
  }
  
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 32d448050bf7..5f036e991937 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -497,6 +497,38 @@ static inline void iommu_iotlb_sync(struct iommu_domain *domain,
  	iommu_iotlb_gather_init(iotlb_gather);
  }
  
+/**
+ * iommu_iotlb_gather_add_range - Gather for address-based TLB invalidation
+ * @gather: TLB gather data
+ * @iova: start of page to invalidate
+ * @size: size of page to invalidate
+ *
+ * Helper for IOMMU drivers to build arbitrarily-sized invalidation commands
+ * where only the address range matters, and simply minimising intermediate
+ * syncs is preferred.
+ */
+static inline void iommu_iotlb_gather_add_range(struct iommu_iotlb_gather *gather,
+						unsigned long iova, size_t size)
+{
+	unsigned long end = iova + size - 1;
+
+	if (gather->start > iova)
+		gather->start = iova;
+	if (gather->end < end)
+		gather->end = end;
+}
+
+/**
+ * iommu_iotlb_gather_add_page - Gather for page-based TLB invalidation
+ * @domain: IOMMU domain to be invalidated
+ * @gather: TLB gather data
+ * @iova: start of page to invalidate
+ * @size: size of page to invalidate
+ *
+ * Helper for IOMMU drivers to build invalidation commands based on individual
+ * pages, or with page size/table level hints which cannot be gathered if they
+ * differ.
+ */
  static inline void iommu_iotlb_gather_add_page(struct iommu_domain *domain,
  					       struct iommu_iotlb_gather *gather,
  					       unsigned long iova, size_t size)
-- 
2.25.1