linux-kernel - Re: [PATCH] iommu/vt-d: Fix to flush cache of PASID directory table

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Date:   Fri, 16 Jun 2023 10:01:45 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Yanfei Xu <yanfei.xu@...el.com>, dwmw2@...radead.org,
        joro@...tes.org, will@...nel.org, robin.murphy@....com
Cc:     baolu.lu@...ux.intel.com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/vt-d: Fix to flush cache of PASID directory table

On 6/15/23 3:16 PM, Yanfei Xu wrote:
> Even the PCI devices don't support pasid capability, PASID
> table is mandatory for a PCI device in scalable mode. However
> flushing cache of pasid directory table for these devices are
> not taken after pasid table is allocated as the "size" of
> table is zero. Fix to assign it with a page size.

Documentation/process/submitting-patches.rst

Please add more information about

- Describe your problem.
- Any background of the problem?
- How your change fixes the problem.
...

> 
> Fixes: 194b3348bdbb ("iommu/vt-d: Fix PASID directory pointer coherency")

Do you need a Cc stable?

> Signed-off-by: Yanfei Xu <yanfei.xu@...el.com>
> ---
>   drivers/iommu/intel/pasid.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
> index c5d479770e12..bde7df055865 100644
> --- a/drivers/iommu/intel/pasid.c
> +++ b/drivers/iommu/intel/pasid.c
> @@ -115,7 +115,9 @@ int intel_pasid_alloc_table(struct device *dev)
>   				  intel_pasid_max_id);
>   
>   	size = max_pasid >> (PASID_PDE_SHIFT - 3);
> -	order = size ? get_order(size) : 0;
> +	if (!size)
> +		size = PAGE_SIZE;
> +	order = get_order(size);
>   	pages = alloc_pages_node(info->iommu->node,
>   				 GFP_KERNEL | __GFP_ZERO, order);
>   	if (!pages) {

Is it similar to

diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
index c5d479770e12..49fc5a038a14 100644
--- a/drivers/iommu/intel/pasid.c
+++ b/drivers/iommu/intel/pasid.c
@@ -129,7 +129,7 @@ int intel_pasid_alloc_table(struct device *dev)
         info->pasid_table = pasid_table;

         if (!ecap_coherent(info->iommu->ecap))
-               clflush_cache_range(pasid_table->table, size);
+               clflush_cache_range(pasid_table->table, (1 << order) * 
PAGE_SIZE);

         return 0;
  }

?

Best regards,
baolu