linux-kernel - RE: [PATCH 2/2] x86/hyperv: Set swiotlb_alloc_from_low

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Date:   Fri, 28 Jan 2022 17:44:54 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Tianyu Lan <ltykernel@...il.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "hch@...radead.org" <hch@...radead.org>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "robin.murphy@....com" <robin.murphy@....com>
CC:     Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        vkuznets <vkuznets@...hat.com>,
        "brijesh.singh@....com" <brijesh.singh@....com>,
        "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
        "hch@....de" <hch@....de>,
        "parri.andrea@...il.com" <parri.andrea@...il.com>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>
Subject: RE: [PATCH 2/2] x86/hyperv: Set swiotlb_alloc_from_low_pages to false

From: Tianyu Lan <ltykernel@...il.com> Sent: Wednesday, January 26, 2022 8:11 AM
> 
> In Hyper-V Isolation VM, swiotlb bnounce buffer size maybe 1G at most
> and there maybe no enough memory from 0 to 4G according to memory layout.
> Devices in Isolation VM can use memory above 4G as DMA memory. Set swiotlb_
> alloc_from_low_pages to false in Isolation VM.
> 
> Signed-off-by: Tianyu Lan <Tianyu.Lan@...rosoft.com>
> ---
>  arch/x86/kernel/cpu/mshyperv.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 5a99f993e639..80a0423ac75d 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -343,6 +343,7 @@ static void __init ms_hyperv_init_platform(void)
>  		 * use swiotlb bounce buffer for dma transaction.
>  		 */
>  		swiotlb_force = SWIOTLB_FORCE;
> +		swiotlb_alloc_from_low_pages = false;
>  #endif
>  	}
> 
> --
> 2.25.1

Reviewed-by: Michael Kelley <mikelley@...rosoft.com>