linux-kernel - Re: [PATCH 5.10 392/530] iommu/vt-d: Preset Access/Dirty bits for IOVA over FL

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Date:   Mon, 17 May 2021 10:38:42 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Wolfgang Müller <wolf@...ole.systems>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     baolu.lu@...ux.intel.com, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Ashok Raj <ashok.raj@...el.com>,
        Joerg Roedel <jroedel@...e.de>, Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 5.10 392/530] iommu/vt-d: Preset Access/Dirty bits for
 IOVA over FL

Hi Wolfgang,

On 5/15/21 9:28 PM, Wolfgang Müller wrote:
> Hi!
> 
> First of all, apologies if this is the wrong place to post a problem
> report. I figured since I was going to reference a particular commit
> anyway I might as well reply to the patch series that (seemed to have)
> introduced the problem.
> 
>> From: Lu Baolu <baolu.lu@...ux.intel.com>
>>
>> [ Upstream commit a8ce9ebbecdfda3322bbcece6b3b25888217f8e3 ]
>>
>> The Access/Dirty bits in the first level page table entry will be set
>> whenever a page table entry was used for address translation or write
>> permission was successfully translated. This is always true when using
>> the first-level page table for kernel IOVA. Instead of wasting hardware
>> cycles to update the certain bits, it's better to set them up at the
>> beginning.
> 
> This commit seems to trigger a kernel panic very early in boot for me in
> 5.10.37 (36 is fine):

It seems due to the back-ported patch:

-	if (!sg) {
-		sg_res = nr_pages;
-		pteval = ((phys_addr_t)phys_pfn << VTD_PAGE_SHIFT) | attr;
+		if (domain->domain.type == IOMMU_DOMAIN_DMA) {
+			attr |= DMA_FL_PTE_ACCESS;
+			if (prot & DMA_PTE_WRITE)
+				attr |= DMA_FL_PTE_DIRTY;
+		}
  	}

+	pteval = ((phys_addr_t)phys_pfn << VTD_PAGE_SHIFT) | attr;

Greg, do you want me to rework this patch, or submit an incremental fix?

Best regards,
baolu