Re: [PATCH v2 5/6] platform/x86: intel_tdx_attest: Add TDX Guest attestation interface driver

[Dave Hansen]

On 7/8/21 3:21 PM, Andy Lutomirski wrote:
>> +		ret = set_memory_decrypted((unsigned long)file->private_data,
>> +					   1UL << get_order(QUOTE_SIZE));
>> +		if (ret)
>> +			break;
> Now private_data is decrypted.  (And this operation is *expensive*.  Why
> is it done at ioctl time?)

Expensive and permanently fractures the direct map.

I'm struggling to figure out why the direct map is even touched here.
Why not just use a vmalloc area mapping?  You really just need *a*
decrypted mapping to the page.  You don't need to make *every* mapping
to the page decrypted.