[Xen-devel] [PATCH] IOMMU/x86: don't bypass softirq processing in arch_iommu_hwdom_init()

[Xen-devel] [PATCH] IOMMU/x86: don't bypass softirq processing in arch_iommu_hwdom_init()

[Jan Beulich]

Even when a page doesn't need mapping, we should check whether softirq
processing should be invoked. Otherwise with sufficiently much RAM
chances of a to-be-mapped page actually occurring with the loop counter
having the "right" value may become diminishingly small.

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/drivers/passthrough/x86/iommu.c
+++ b/xen/drivers/passthrough/x86/iommu.c
@@ -226,9 +226,8 @@ void __hwdom_init arch_iommu_hwdom_init(
         int rc;
 
         if ( !hwdom_iommu_map(d, pfn, max_pfn) )
-            continue;
-
-        if ( paging_mode_translate(d) )
+            rc = 0;
+        else if ( paging_mode_translate(d) )
             rc = set_identity_p2m_entry(d, pfn, p2m_access_rw, 0);
         else
             rc = iommu_map(d, _dfn(pfn), _mfn(pfn), PAGE_ORDER_4K,

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Re: [Xen-devel] [PATCH] IOMMU/x86: don't bypass softirq processing in arch_iommu_hwdom_init()

[Roger Pau Monné]

On Mon, Mar 02, 2020 at 10:49:48AM +0100, Jan Beulich wrote:
> Even when a page doesn't need mapping, we should check whether softirq
> processing should be invoked. Otherwise with sufficiently much RAM
> chances of a to-be-mapped page actually occurring with the loop counter
> having the "right" value may become diminishingly small.
> 
> Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

Thanks, Roger.

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Re: [Xen-devel] [PATCH] IOMMU/x86: don't bypass softirq processing in arch_iommu_hwdom_init()

[Andrew Cooper]

On 02/03/2020 09:55, Roger Pau Monné wrote:
> On Mon, Mar 02, 2020 at 10:49:48AM +0100, Jan Beulich wrote:
>> Even when a page doesn't need mapping, we should check whether softirq
>> processing should be invoked. Otherwise with sufficiently much RAM
>> chances of a to-be-mapped page actually occurring with the loop counter
>> having the "right" value may become diminishingly small.
>>
>> Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

Tested-by: Andrew Cooper <andrew.cooper3@citrix.com>

This resolves the watchdog timeout, and reveals more work to do, but
I'll follow up on the main thread.

~Andrew

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