Re: [PATCH 3/4 V3] Remap the device table of IOMMU in encrypted manner for kdump

Tom Lendacky
2018-06-20T16:42:33Z

On 6/16/2018 3:27 AM, Lianbo Jiang wrote:
> In kdump mode, it will copy the device table of IOMMU from the old
> device table, which is encrypted when SME is enabled in the first
> kernel. So we must remap it in encrypted manner in order to be
> automatically decrypted when we read.
>
> Signed-off-by: Lianbo Jiang <lijiang@redhat.com>
> ---
> Some changes:
> 1. add some comments
> 2. clean compile warning.
>
> drivers/iommu/amd_iommu_init.c | 15 ++++++++++++++-
> 1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
> index 904c575..a20af4c 100644
> --- a/drivers/iommu/amd_iommu_init.c
> +++ b/drivers/iommu/amd_iommu_init.c
> @@ -889,11 +889,24 @@ static bool copy_device_table(void)
> }
>
> old_devtb_phys = entry & PAGE_MASK;
> +
> + /*
> + * When sme enable in the first kernel, old_devtb_phys includes the
> + * memory encryption mask(sme_me_mask), we must remove the memory
> + * encryption mask to obtain the true physical address in kdump mode.
> + */
> + if (mem_encrypt_active() && is_kdump_kernel())
> + old_devtb_phys = __sme_clr(old_devtb_phys);
> +

You can probably just use "if (is_kdump_kernel())" here, since memory
encryption is either on in both the first and second kernel or off in
both the first and second kernel. At which point __sme_clr() will do
the proper thing.

Actually, this needs to be done no matter what. When doing either the
ioremap_encrypted() or the memremap(), the physical address should not
include the encryption bit/mask.

Thanks,
Tom

> if (old_devtb_phys >= 0x100000000ULL) {
> pr_err("The address of old device table is above 4G, not trustworthy!\n");
> return false;
> }
> - old_devtb = memremap(old_devtb_phys, dev_table_size, MEMREMAP_WB);
> + old_devtb = (mem_encrypt_active() && is_kdump_kernel())
> + ? (__force void *)ioremap_encrypted(old_devtb_phys,
> + dev_table_size)
> + : memremap(old_devtb_phys, dev_table_size, MEMREMAP_WB);> +
> if (!old_devtb)
> return false;
>
>