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

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Date:   Tue, 3 May 2022 15:28:47 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Kai Huang <kai.huang@...el.com>
Cc:     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 5/3/22 3:24 PM, Dave Hansen wrote:
> 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?

I have already implemented it and testing it now.

In this discussion, we are comparing the use of DMA API for memory
allocation vs vmap/sharing it in driver itself.

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer