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

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Date:   Thu, 21 Jun 2018 13:42:24 +0800
From:   lijiang <lijiang@...hat.com>
To:     Tom Lendacky <thomas.lendacky@....com>,
        linux-kernel@...r.kernel.org
Cc:     iommu@...ts.linux-foundation.org, kexec@...ts.infradead.org,
        dyoung@...hat.com
Subject: Re: [PATCH 3/4 V3] Remap the device table of IOMMU in encrypted
 manner for kdump

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@...hat.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;
>>  
>>