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

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Date:   Tue, 22 Feb 2022 09:05:43 +0100
From:   Christoph Hellwig <hch@....de>
To:     Tianyu Lan <ltykernel@...il.com>
Cc:     Christoph Hellwig <hch@....de>, 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 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.