David, Any comments on this patch? Thanks, Alex On Tue, 2013-10-29 at 10:21 -0600, Alex Williamson wrote: > The setting of the SNP bit in the intel-iommu page tables should not > be dependent on the current capability of the iommu domain. The > current VT-d spec (2.2) indicates the SNP bit is "treated as > reserved[0] by hardware implementations not supporting Snoop Control". > Furthermore, section 3.7.3 indicates: > > If the Snoop Control (SC) field in extended capability Register is > reported as 0, snoop behavior for access to the page mapped through > second-level translation is determined by the no-snoop attribute in > the request. > > This all seems to indicate that hardware incapable of Snoop Control > will handle the SNP bit as zero regardless of the value stored in > the PTE. > > The trouble with the current implementation is that mapping flags > depend on the state of the iommu domain at the time of the mapping, > yet no attempt is made to update existing mappings when the iommu > domain composition changes. This leaves the iommu domain in a state > where some mappings may enforce coherency, others do not, and the user > of the IOMMU API has no ability to later enable the desired flags > atomically with respect to DMA. > > If we always honor the IOMMU_CACHE flag then an IOMMU API user who > specifies IOMMU_CACHE for all mappings can assume that the coherency > of the mappings within a domain follow the coherency capability of > the domain itself. > > Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx> > --- > drivers/iommu/intel-iommu.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c > index 15e9b57..c46c6a6 100644 > --- a/drivers/iommu/intel-iommu.c > +++ b/drivers/iommu/intel-iommu.c > @@ -4084,7 +4084,7 @@ static int intel_iommu_map(struct iommu_domain *domain, > prot |= DMA_PTE_READ; > if (iommu_prot & IOMMU_WRITE) > prot |= DMA_PTE_WRITE; > - if ((iommu_prot & IOMMU_CACHE) && dmar_domain->iommu_snooping) > + if (iommu_prot & IOMMU_CACHE) > prot |= DMA_PTE_SNP; > > max_addr = iova + size; > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
