From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D7974C48BDF for ; Tue, 15 Jun 2021 12:55:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BA02261466 for ; Tue, 15 Jun 2021 12:55:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230383AbhFOM5i (ORCPT ); Tue, 15 Jun 2021 08:57:38 -0400 Received: from foss.arm.com ([217.140.110.172]:34686 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231145AbhFOM5c (ORCPT ); Tue, 15 Jun 2021 08:57:32 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 0B8A811D4; Tue, 15 Jun 2021 05:55:25 -0700 (PDT) Received: from [10.57.9.136] (unknown [10.57.9.136]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E3D173F719; Tue, 15 Jun 2021 05:55:23 -0700 (PDT) Subject: Re: [PATCH v3 5/6] iommu/amd: Tailored gather logic for AMD To: Nadav Amit , Joerg Roedel Cc: linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, Nadav Amit , Jiajun Cao , Will Deacon References: <20210607182541.119756-1-namit@vmware.com> <20210607182541.119756-6-namit@vmware.com> From: Robin Murphy Message-ID: <1913c012-e6c0-1d5e-01b3-5f6da367c6bd@arm.com> Date: Tue, 15 Jun 2021 13:55:18 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <20210607182541.119756-6-namit@vmware.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-06-07 19:25, Nadav Amit wrote: > 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 or page-size changes > are 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 page-size changes > and 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. Also check whether the new > region would cause IOTLB invalidation of large region that would include > unmodified PTE. The latter check is done according to the "order" of the > IOTLB flush. If it helps, Reviewed-by: Robin Murphy I wonder if it might be more effective to defer the alignment-based splitting part to amd_iommu_iotlb_sync() itself, but that could be investigated as another follow-up. Robin. > Cc: Joerg Roedel > Cc: Will Deacon > Cc: Jiajun Cao > Cc: Robin Murphy > Cc: Lu Baolu > Cc: iommu@lists.linux-foundation.org > Cc: linux-kernel@vger.kernel.org> > Signed-off-by: Nadav Amit > --- > drivers/iommu/amd/iommu.c | 44 ++++++++++++++++++++++++++++++++++++++- > 1 file changed, 43 insertions(+), 1 deletion(-) > > diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c > index 3e40f6610b6a..128f2e889ced 100644 > --- a/drivers/iommu/amd/iommu.c > +++ b/drivers/iommu/amd/iommu.c > @@ -2053,6 +2053,48 @@ 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 && gather->end != 0) { > + unsigned long start = iova, end = start + size - 1; > + > + if (iommu_iotlb_gather_is_disjoint(gather, iova, size)) { > + /* > + * If the new page is disjoint from the current range, > + * flush. > + */ > + iommu_iotlb_sync(domain, gather); > + } else { > + /* > + * If the order of TLB flushes increases by more than > + * 1, it means that we would have to flush PTEs that > + * were not modified. In this case, flush. > + */ > + unsigned long new_start = min(gather->start, start); > + unsigned long new_end = min(gather->end, end); > + int msb_diff = fls64(gather->end ^ gather->start); > + int new_msb_diff = fls64(new_end ^ new_start); > + > + if (new_msb_diff > msb_diff + 1) > + 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) > @@ -2067,7 +2109,7 @@ 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; > } >