From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [RFC] vfio/type1: handle case where IOMMU does not support PAGE_SIZE size Date: Wed, 28 Oct 2015 17:55:34 +0000 Message-ID: <20151028175533.GM18966@arm.com> References: <1446037965-2341-1-git-send-email-eric.auger@linaro.org> <1446049648.8018.397.camel@redhat.com> <563101A0.7020404@linaro.org> <1446053858.8018.406.camel@redhat.com> <56310A79.4020309@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Alex Williamson , eric.auger@st.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, suravee.suthikulpanit@amd.com, christoffer.dall@linaro.org, linux-kernel@vger.kernel.org, patches@linaro.org To: Eric Auger Return-path: Content-Disposition: inline In-Reply-To: <56310A79.4020309@linaro.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Wed, Oct 28, 2015 at 06:48:41PM +0100, Eric Auger wrote: > On 10/28/2015 06:37 PM, Alex Williamson wrote: > > Ok, so with hopefully correcting my understand of what this does, isn't > > this effectively the same: > > > > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c > > index 57d8c37..7db4f5a 100644 > > --- a/drivers/vfio/vfio_iommu_type1.c > > +++ b/drivers/vfio/vfio_iommu_type1.c > > @@ -403,13 +403,19 @@ static void vfio_remove_dma(struct vfio_iommu *iommu, stru > > static unsigned long vfio_pgsize_bitmap(struct vfio_iommu *iommu) > > { > > struct vfio_domain *domain; > > - unsigned long bitmap = PAGE_MASK; > > + unsigned long bitmap = ULONG_MAX; > > > > mutex_lock(&iommu->lock); > > list_for_each_entry(domain, &iommu->domain_list, next) > > bitmap &= domain->domain->ops->pgsize_bitmap; > > mutex_unlock(&iommu->lock); > > > > + /* Some comment about how the IOMMU API splits requests */ > > + if (bitmap & ~PAGE_MASK) { > > + bitmap &= PAGE_MASK; > > + bitmap |= PAGE_SIZE; > > + } > > + > > return bitmap; > > } > Yes, to me it is indeed the same > > > > This would also expose to the user that we're accepting PAGE_SIZE, which > > we weren't before, so it was not quite right to just let them do it > > anyway. I don't think we even need to get rid of the WARN_ONs, do we? > > Thanks, > > The end-user might be afraid of those latter. Personally I would get rid > of them but that's definitively up to you. I think Alex's point is that the WARN_ON's won't trigger with this patch, because he clears those lower bits in the bitmap. Will