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

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Date:   Tue, 22 Feb 2022 23:07:19 +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 2/22/2022 4:05 PM, Christoph Hellwig wrote:
> On Mon, Feb 21, 2022 at 11:14:58PM +0800, Tianyu Lan wrote:
>> Sorry. The boot failure is not related with these patches and the issue
>> has been fixed in the latest upstream code.
>>
>> There is a performance bottleneck due to io tlb mem's spin lock during
>> performance test. All devices'io queues uses same io tlb mem entry
>> and the spin lock of io tlb mem introduce overheads. There is a fix patch
>> from Andi Kleen in the github. Could you have a look?
>>
>> https://github.com/intel/tdx/commit/4529b5784c141782c72ec9bd9a92df2b68cb7d45
> 
> Please post these things to the list.
> 
> But I suspect the right answer for the "secure" hypervisor case is to
> use the per-device swiotlb regions that we've recently added.

Thanks for your comment. That means we need to expose an 
swiotlb_device_init() interface to allocate bounce buffer and initialize
io tlb mem entry. DMA API Current  rmem_swiotlb_device_init() only works
for platform with device tree. The new API should be called in the bus
driver or new DMA API. Could you check whether this is a right way 
before we start the work.

Thanks.