From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Murphy Subject: Re: [PATCH 6/9] iommu/amd: Implement map_atomic Date: Tue, 16 Apr 2019 15:13:16 +0100 Message-ID: <78f2114b-0dcb-2dcf-c3b3-411e064b079f@arm.com> References: <20190411184741.27540-1-tmurphy@arista.com> <20190411184741.27540-7-tmurphy@arista.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20190411184741.27540-7-tmurphy@arista.com> Content-Language: en-GB Sender: linux-kernel-owner@vger.kernel.org To: Tom Murphy , iommu@lists.linux-foundation.org Cc: dima@arista.com, jamessewart@arista.com, murphyt7@tcd.ie, Joerg Roedel , Will Deacon , Marek Szyprowski , Kukjin Kim , Krzysztof Kozlowski , Matthias Brugger , Andy Gross , David Brown , Rob Clark , Heiko Stuebner , Marc Zyngier , Thomas Gleixner , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-mediatek@lists.infradead.org, linux-arm-msm@vger.kernel.org, linux-rockchip@lists.infradead.org List-Id: linux-rockchip.vger.kernel.org On 11/04/2019 19:47, Tom Murphy wrote: > Instead of using a spin lock I removed the mutex lock from both the > amd_iommu_map and amd_iommu_unmap path as well. iommu_map doesn’t lock > while mapping and so if iommu_map is called by two different threads on > the same iova region it results in a race condition even with the locks. > So the locking in amd_iommu_map and amd_iommu_unmap doesn't add any real > protection. The solution to this is for whatever manages the allocated > iova’s externally to make sure iommu_map isn’t called twice on the same > region at the same time. Note that that assumption is not necessarily sufficient - even with correct address space management you can have cases like two threads mapping adjacent pages, where even thought they are targeting different PTEs they can race to install/modify intermediate levels of the pagetable. I believe AMD is actually OK in that regard, but some drivers *are* relying on locking for correctness so it can't just be unequivocally removed everywhere. Robin. > Signed-off-by: Tom Murphy > --- > drivers/iommu/amd_iommu.c | 25 ++++++++++++++++++------- > 1 file changed, 18 insertions(+), 7 deletions(-) > > diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c > index 2d4ee10626b4..b45e0e033adc 100644 > --- a/drivers/iommu/amd_iommu.c > +++ b/drivers/iommu/amd_iommu.c > @@ -3089,12 +3089,12 @@ static int amd_iommu_attach_device(struct iommu_domain *dom, > return ret; > } > > -static int amd_iommu_map(struct iommu_domain *dom, unsigned long iova, > - phys_addr_t paddr, size_t page_size, int iommu_prot) > +static int __amd_iommu_map(struct iommu_domain *dom, unsigned long iova, > + phys_addr_t paddr, size_t page_size, int iommu_prot, > + gfp_t gfp) > { > struct protection_domain *domain = to_pdomain(dom); > int prot = 0; > - int ret; > > if (domain->mode == PAGE_MODE_NONE) > return -EINVAL; > @@ -3104,11 +3104,21 @@ static int amd_iommu_map(struct iommu_domain *dom, unsigned long iova, > if (iommu_prot & IOMMU_WRITE) > prot |= IOMMU_PROT_IW; > > - mutex_lock(&domain->api_lock); > - ret = iommu_map_page(domain, iova, paddr, page_size, prot, GFP_KERNEL); > - mutex_unlock(&domain->api_lock); > + return iommu_map_page(domain, iova, paddr, page_size, prot, gfp); > +} > > - return ret; > +static int amd_iommu_map(struct iommu_domain *dom, unsigned long iova, > + phys_addr_t paddr, size_t page_size, int iommu_prot) > +{ > + return __amd_iommu_map(dom, iova, paddr, page_size, iommu_prot, > + GFP_KERNEL); > +} > + > +static int amd_iommu_map_atomic(struct iommu_domain *dom, unsigned long iova, > + phys_addr_t paddr, size_t page_size, int iommu_prot) > +{ > + return __amd_iommu_map(dom, iova, paddr, page_size, iommu_prot, > + GFP_ATOMIC); > } > > static size_t amd_iommu_unmap(struct iommu_domain *dom, unsigned long iova, > @@ -3262,6 +3272,7 @@ const struct iommu_ops amd_iommu_ops = { > .attach_dev = amd_iommu_attach_device, > .detach_dev = amd_iommu_detach_device, > .map = amd_iommu_map, > + .map_atomic = amd_iommu_map_atomic, > .unmap = amd_iommu_unmap, > .iova_to_phys = amd_iommu_iova_to_phys, > .add_device = amd_iommu_add_device, >