From mboxrd@z Thu Jan 1 00:00:00 1970 From: Baoquan He Subject: Re: [PATCH v9 10/13] iommu/amd: Allocate memory below 4G for dev table if translation pre-enabled Date: Fri, 4 Aug 2017 21:01:12 +0800 Message-ID: <20170804130112.GM1874@x1> References: <1501587449-9817-1-git-send-email-bhe@redhat.com> <1501587449-9817-11-git-send-email-bhe@redhat.com> <20170804122524.GV3431@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20170804122524.GV3431-l3A5Bk7waGM@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Joerg Roedel Cc: iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: iommu@lists.linux-foundation.org On 08/04/17 at 02:25pm, Joerg Roedel wrote: > On Tue, Aug 01, 2017 at 07:37:26PM +0800, Baoquan He wrote: > > AMD pointed out it's unsafe to update the device-table while iommu > > is enabled. It turns out that device-table pointer update is split > > up into two 32bit writes in the IOMMU hardware. So updating it while > > the IOMMU is enabled could have some nasty side effects. > > > > The safe way to work around this is to always allocate the device-table > > below 4G, including the old device-table in normal kernel and the > > device-table used for copying the content of the old device-table in kdump > > kernel. Meanwhile we need check if the address of old device-table is > > above 4G because it might has been touched accidentally in corrupted > > 1st kernel. > > > > Signed-off-by: Baoquan He > > --- > > drivers/iommu/amd_iommu_init.c | 9 +++++++-- > > 1 file changed, 7 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c > > index 6a77b99d08e4..8c6431ac5698 100644 > > --- a/drivers/iommu/amd_iommu_init.c > > +++ b/drivers/iommu/amd_iommu_init.c > > @@ -882,11 +882,15 @@ static int copy_device_table(void) > > continue; > > > > old_devtb_phys = entry & PAGE_MASK; > > + if (old_devtb_phys > 0x100000000ULL) { > > Needs to be '>='. Will change. > > > + pr_err("The address of old device table is above 4G, not trustworthy!/n"); > > + return -1; > > + } > > Okay, forget my previous comment about it, the check is added here >