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Re: [Xen-devel] [PATCH] gnttab: make sure grant map operations don't skip their IOMMU part
- To: "Durrant, Paul" <pdurrant@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Fri, 29 Nov 2019 19:15:10 +0000
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- Cc: Juergen Gross <jgross@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Wei Liu <wl@xxxxxxx>, Konrad Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxx>
- Delivery-date: Fri, 29 Nov 2019 19:15:26 +0000
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On 22/11/2019 11:22, Durrant, Paul wrote:
>> @@ -1144,27 +1140,22 @@ map_grant_ref(
>> if ( need_iommu )
>> {
>> unsigned int kind;
>> - int err = 0;
>>
>> double_gt_lock(lgt, rgt);
>>
>> - /* We're not translated, so we know that gmfns and mfns are
>> - the same things, so the IOMMU entry is always 1-to-1. */
>> + /*
>> + * We're not translated, so we know that dfns and mfns are
>> + * the same things, so the IOMMU entry is always 1-to-1.
>> + */
>> kind = mapkind(lgt, rd, mfn);
>> - if ( (act_pin & (GNTPIN_hstw_mask|GNTPIN_devw_mask)) &&
>> - !(old_pin & (GNTPIN_hstw_mask|GNTPIN_devw_mask)) )
>> - {
>> - if ( !(kind & MAPKIND_WRITE) )
>> - err = iommu_legacy_map(ld, _dfn(mfn_x(mfn)), mfn, 0,
>> - IOMMUF_readable |
>> IOMMUF_writable);
>> - }
>> - else if ( act_pin && !old_pin )
>> - {
>> - if ( !kind )
>> - err = iommu_legacy_map(ld, _dfn(mfn_x(mfn)), mfn, 0,
>> - IOMMUF_readable);
>> - }
>> - if ( err )
>> + if ( !(op->flags & GNTMAP_readonly) &&
>> + !(kind & MAPKIND_WRITE) )
>> + kind = IOMMUF_readable | IOMMUF_writable;
>> + else if ( !kind )
>> + kind = IOMMUF_readable;
>> + else
>> + kind = 0;
>> + if ( kind && iommu_legacy_map(ld, _dfn(mfn_x(mfn)), mfn, 0, kind)
> Re-using 'kind' in this way slightly obfuscates things. I'm sure the compiler
> would still generate reasonable code if you used a separate 'flags' variable
> within the same scope.
I agree.
Everything LGTM, so Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
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