linux-kernel - Re: [PATCH V6 3/5] hyper-v: Enable swiotlb bounce buffer for Isolation VM

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Date:   Fri, 10 Dec 2021 22:01:16 +0800
From:   Tianyu Lan <ltykernel@...il.com>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.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>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "hch@...radead.org" <hch@...radead.org>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>
Cc:     "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...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>, "joro@...tes.org" <joro@...tes.org>,
        "parri.andrea@...il.com" <parri.andrea@...il.com>,
        "dave.hansen@...el.com" <dave.hansen@...el.com>
Subject: Re: [PATCH V6 3/5] hyper-v: Enable swiotlb bounce buffer for
 Isolation VM



On 12/10/2021 9:25 PM, Tianyu Lan wrote:
>>> @@ -319,8 +320,16 @@ static void __init ms_hyperv_init_platform(void)
>>>           pr_info("Hyper-V: Isolation Config: Group A 0x%x, Group B 
>>> 0x%x\n",
>>>               ms_hyperv.isolation_config_a, 
>>> ms_hyperv.isolation_config_b);
>>>
>>> -        if (hv_get_isolation_type() == HV_ISOLATION_TYPE_SNP)
>>> +        if (hv_get_isolation_type() == HV_ISOLATION_TYPE_SNP) {
>>>               static_branch_enable(&isolation_type_snp);
>>> +            swiotlb_unencrypted_base = ms_hyperv.shared_gpa_boundary;
>>> +        }
>>> +
>>> +        /*
>>> +         * Enable swiotlb force mode in Isolation VM to
>>> +         * use swiotlb bounce buffer for dma transaction.
>>> +         */
>>> +        swiotlb_force = SWIOTLB_FORCE;
>> I'm good with this approach that directly updates the swiotlb settings 
>> here
>>
>> rather than in IOMMU initialization code.  It's a lot more 
>> straightforward.
>>
>> However, there's an issue if building for X86_32 without PAE, in that the
>> swiotlb module may not be built, resulting in compile and link 
>> errors.  The
>> swiotlb.h file needs to be updated to provide a stub function for
>> swiotlb_update_mem_attributes().   swiotlb_unencrypted_base probably
>> needs wrapper functions to get/set it, which can be stubs when
>> CONFIG_SWIOTLB is not set.  swiotlb_force is a bit of a mess in that 
>> it already
>> has a stub definition that assumes it will only be read, and not set.  
>> A bit of
>> thinking will be needed to sort that out.
> 
> It's ok to fix the issue via selecting swiotlb when CONFIG_HYPERV is
> set?
> 
Sorry. ignore the previous statement. These codes doesn't depend on 
CONFIG_HYPERV.

How about making these code under #ifdef CONFIG_X86_64 or CONFIG_SWIOTLB?