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Fri, 23 Jul 2021 10:02:05 -0700 (PDT) From: Nadav Amit X-Google-Original-From: Nadav Amit To: Joerg Roedel Subject: [PATCH v6 5/7] iommu/amd: Tailored gather logic for AMD Date: Fri, 23 Jul 2021 02:32:07 -0700 Message-Id: <20210723093209.714328-6-namit@vmware.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210723093209.714328-1-namit@vmware.com> References: <20210723093209.714328-1-namit@vmware.com> MIME-Version: 1.0 Cc: Robin Murphy , linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, Nadav Amit , Jiajun Cao , Will Deacon X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" From: Nadav Amit AMD's IOMMU can flush efficiently (i.e., in a single flush) any range. This is in contrast, for instnace, to Intel IOMMUs that have a limit on the number of pages that can be flushed in a single flush. In addition, AMD's IOMMU do not care about the page-size, so changes of the page size do not need to trigger a TLB flush. So in most cases, a TLB flush due to disjoint range is not needed for AMD. Yet, vIOMMUs require the hypervisor to synchronize the virtualized IOMMU's PTEs with the physical ones. This process induce overheads, so it is better not to cause unnecessary flushes, i.e., flushes of PTEs that were not modified. Implement and use amd_iommu_iotlb_gather_add_page() and use it instead of the generic iommu_iotlb_gather_add_page(). Ignore disjoint regions unless "non-present cache" feature is reported by the IOMMU capabilities, as this is an indication we are running on a physical IOMMU. A similar indication is used by VT-d (see "caching mode"). The new logic retains the same flushing behavior that we had before the introduction of page-selective IOTLB flushes for AMD. On virtualized environments, check if the newly flushed region and the gathered one are disjoint and flush if it is. Cc: Joerg Roedel Cc: Will Deacon Cc: Jiajun Cao Cc: Lu Baolu Cc: iommu@lists.linux-foundation.org Cc: linux-kernel@vger.kernel.org> Reviewed-by: Robin Murphy Signed-off-by: Nadav Amit --- drivers/iommu/amd/iommu.c | 23 ++++++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-) diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c index bfae3928b98f..f5d5f2124391 100644 --- a/drivers/iommu/amd/iommu.c +++ b/drivers/iommu/amd/iommu.c @@ -2048,6 +2048,27 @@ static int amd_iommu_map(struct iommu_domain *dom, unsigned long iova, return ret; } +static void amd_iommu_iotlb_gather_add_page(struct iommu_domain *domain, + struct iommu_iotlb_gather *gather, + unsigned long iova, size_t size) +{ + /* + * AMD's IOMMU can flush as many pages as necessary in a single flush. + * Unless we run in a virtual machine, which can be inferred according + * to whether "non-present cache" is on, it is probably best to prefer + * (potentially) too extensive TLB flushing (i.e., more misses) over + * mutliple TLB flushes (i.e., more flushes). For virtual machines the + * hypervisor needs to synchronize the host IOMMU PTEs with those of + * the guest, and the trade-off is different: unnecessary TLB flushes + * should be avoided. + */ + if (amd_iommu_np_cache && + iommu_iotlb_gather_is_disjoint(gather, iova, size)) + iommu_iotlb_sync(domain, gather); + + iommu_iotlb_gather_add_range(gather, iova, size); +} + static size_t amd_iommu_unmap(struct iommu_domain *dom, unsigned long iova, size_t page_size, struct iommu_iotlb_gather *gather) @@ -2062,7 +2083,7 @@ static size_t amd_iommu_unmap(struct iommu_domain *dom, unsigned long iova, r = (ops->unmap) ? ops->unmap(ops, iova, page_size, gather) : 0; - iommu_iotlb_gather_add_page(dom, gather, iova, page_size); + amd_iommu_iotlb_gather_add_page(dom, gather, iova, page_size); return r; } -- 2.25.1 _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu