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

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Date:   Tue, 3 May 2022 15:30:19 -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 3:28 PM, Sathyanarayanan Kuppuswamy wrote:
> 
> 
> 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.

I mean, I have already implemented the vmap based solution.

> 
> 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