Re: [PATCH v9 10/13] iommu/amd: Allocate memory below 4G for dev table if translation pre-enabled

Baoquan He
2017-08-04T13:01:17Z

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 <bhe@redhat.com>
> > ---
> > 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
>