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

lijiang
2018-06-21T05:42:36Z

在 2018年06月21日 00:42, Tom Lendacky 写道:
> 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
>
Thanks for your comments. If we don't remove the memory encryption mask, it will
return false because the 'old_devtb_phys >= 0x100000000ULL' may become true.

Lianbo
>> 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;
>>
>>