linux-kernel - Re: [PATCH v5 3/3] x86/tdx: Add Quote generation support

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Date:   Tue, 3 May 2022 15:24:05 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Kai Huang <kai.huang@...el.com>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Wander Lairson Costa <wander@...hat.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/3] x86/tdx: Add Quote generation support

On 5/2/22 18:27, Kirill A. Shutemov wrote:
>> Again, Dave and Andi already commented you should use vmap() to avoid breaking
>> up the direct-mapping.  Please use vmap() instead.
>>
>> https://lore.kernel.org/all/ce0feeec-a949-35f8-3010-b0d69acbbc2e@linux.intel.com/
>>
>> Will review the rest later.
> I would rather convert it to use DMA API for memory allocation. It will
> tap into swiotlb buffer that already converted and there's no need to
> touch direct mapping. Both allocation and freeing such memory is cheaper
> because of that.

Sathya, I don't quite understand why you are so forcefully declining to
incorporate review feedback on this point.  I gave very specific
feedback about the kind of mapping you need and that you should avoid
fragmenting the direct map if at all possible.

Why is this code still fragmenting the direct map?