linux-kernel - Re: [PATCH 0/2] x86/hyperv/Swiotlb: Add swiotlb_alloc_from_low

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Date:   Wed, 2 Feb 2022 13:22:46 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@...radead.org>,
        Tianyu Lan <ltykernel@...il.com>
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, m.szyprowski@...sung.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, hch@....de,
        parri.andrea@...il.com, thomas.lendacky@....com
Subject: Re: [PATCH 0/2] x86/hyperv/Swiotlb: Add swiotlb_alloc_from_low_pages
 switch

On 2022-02-02 08:12, Christoph Hellwig wrote:
> I think this interface is a little too hacky.  In the end all the
> non-trusted hypervisor schemes (including the per-device swiotlb one)
> can allocate the memory from everywhere and want for force use of
> swiotlb.  I think we need some kind of proper interface for that instead
> of setting all kinds of global variables.

Right, if platform/hypervisor code knows enough to be able to set magic 
non-standard allocation flags correctly, surely it could equally just 
perform whatever non-standard allocation it needs and call 
swiotlb_init_with_tbl() instead of swiotlb_init().

Robin.