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

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Message-ID: <40f91949-58fa-4be2-5b01-ea34dda58670@gmail.com>
Date:   Wed, 23 Feb 2022 17:46:39 +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 2/23/2022 12:00 AM, Christoph Hellwig wrote:
> On Tue, Feb 22, 2022 at 11:07:19PM +0800, Tianyu Lan wrote:
>> 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.
> 
> Do these VMs use ACPI?  We'd probably really want some kind of higher
> level configuration and not have the drivers request it themselves.

Yes, Hyper-V isolation VM uses ACPI. Devices are enumerated via vmbus 
host and there is no child device information in ACPI table. The host 
driver seems to be the right place to call new API.