Hi Baolu, On Tue, 7 Feb 2023 15:10:48 +0800, Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx> wrote: > On 2023/2/7 1:25, Jacob Pan wrote: > >>> --- > >>> drivers/iommu/intel/iommu.c | 6 ++++++ > >>> 1 file changed, 6 insertions(+) > >>> > >>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c > >>> index 59df7e42fd53..b4878c7ac008 100644 > >>> --- a/drivers/iommu/intel/iommu.c > >>> +++ b/drivers/iommu/intel/iommu.c > >>> @@ -1976,6 +1976,12 @@ static int domain_context_mapping_one(struct > >>> dmar_domain *domain, pds = context_get_sm_pds(table); > >>> context->lo = (u64)virt_to_phys(table->table) | > >>> context_pdts(pds); > >>> + /* > >>> + * Scalable-mode PASID directory pointer is not > >>> snooped if the > >>> + * coherent bit is not set. > >>> + */ > >>> + if (!ecap_coherent(iommu->ecap)) > >>> + clflush_cache_range(table->table, sizeof(void > >>> *)); > >> This isn't comprehensive. The clflush should be called whenever the > >> pasid directory table is allocated or updated. > >> > > allocate a pasid table does not mean it gets used by iommu hw, not > > until it is programmed into context entry. > > Hi Jacob, > > This page is used by the device, and the device's access to this memory > is not coherent. So after the page is allocated, any changes made by the > CPU to this page must be written back to the real memory. > > This patch only flushes the first 8 bytes of the table. That's not > enough. > make sense, thanks for the explanation. > Be aware that page allocation also requires a clflush, because at least > __GFP_ ZERO implies modification to page. > Yes, zeroing dir page does change it but I think if we intercept every update to the directory entry, it should be sufficient? will send an updated version. Thanks, Jacob
