linux-kernel - Re: [PATCH V2 1/2] Swiotlb: Add swiotlb_alloc_from_low

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Message-ID: <8d052867-ccff-f00f-7c89-cc26a4bfa347@gmail.com>
Date:   Tue, 15 Feb 2022 23:32:32 +0800
From:   Tianyu Lan <ltykernel@...il.com>
To:     Christoph Hellwig <hch@....de>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        wei.liu@...nel.org, decui@...rosoft.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, hch@...radead.org,
        m.szyprowski@...sung.com, robin.murphy@....com,
        michael.h.kelley@...rosoft.com,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        iommu@...ts.linux-foundation.org, linux-hyperv@...r.kernel.org,
        linux-kernel@...r.kernel.org, vkuznets@...hat.com,
        brijesh.singh@....com, konrad.wilk@...cle.com,
        parri.andrea@...il.com, thomas.lendacky@....com
Subject: Re: [PATCH V2 1/2] Swiotlb: Add swiotlb_alloc_from_low_pages switch

On 2/14/2022 9:58 PM, Christoph Hellwig wrote:
> On Mon, Feb 14, 2022 at 07:28:40PM +0800, Tianyu Lan wrote:
>> On 2/14/2022 4:19 PM, Christoph Hellwig wrote:
>>> Adding a function to set the flag doesn't really change much.  As Robin
>>> pointed out last time you should fine a way to just call
>>> swiotlb_init_with_tbl directly with the memory allocated the way you
>>> like it.  Or given that we have quite a few of these trusted hypervisor
>>> schemes maybe add an argument to swiotlb_init that specifies how to
>>> allocate the memory.
>>
>> Thanks for your suggestion. I will try the first approach first approach.
> 
> Take a look at the SWIOTLB_ANY flag in this WIP branch:
> 
>     http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/swiotlb-init-cleanup
> 
> That being said I'm not sure that either this flag or the existing powerpc
> code iѕ actually the right thing to do.  We still need the 4G limited
> buffer to support devices with addressing limitations.  So I think we need
> an additional io_tlb_mem instance for the devices without addressing
> limitations instead.
> 

Hi Christoph:
      Thanks for your patches. I tested these patches in Hyper-V trusted 
VM and system can't boot up. I am debugging and will report back.