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

Joerg Roedel
2017-08-04T12:25:28Z

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 '>='.

> + 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