Message-ID: <877e6f24-2004-0681-f9f3-241fb6ace427@gmail.com>
Date:   Sat, 4 Dec 2021 15:26:36 +0800
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Subject: Re: [PATCH V3 3/5] hyperv/IOMMU: Enable swiotlb bounce buffer for
 Isolation VM
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To:     "Michael Kelley (LINUX)" <mikelley@microsoft.com>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        Dexuan Cui <decui@microsoft.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "bp@alien8.de" <bp@alien8.de>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "x86@kernel.org" <x86@kernel.org>, "hpa@zytor.com" <hpa@zytor.com>,
        "jgross@suse.com" <jgross@suse.com>,
        "sstabellini@kernel.org" <sstabellini@kernel.org>,
        "boris.ostrovsky@oracle.com" <boris.ostrovsky@oracle.com>,
        "joro@8bytes.org" <joro@8bytes.org>,
        "will@kernel.org" <will@kernel.org>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "kuba@kernel.org" <kuba@kernel.org>,
        "jejb@linux.ibm.com" <jejb@linux.ibm.com>,
        "martin.petersen@oracle.com" <martin.petersen@oracle.com>,
        "arnd@arndb.de" <arnd@arndb.de>,
        "hch@infradead.org" <hch@infradead.org>,
        "m.szyprowski@samsung.com" <m.szyprowski@samsung.com>,
        "robin.murphy@arm.com" <robin.murphy@arm.com>,
        Tianyu Lan <Tianyu.Lan@microsoft.com>,
        "thomas.lendacky@amd.com" <thomas.lendacky@amd.com>,
        "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc:     "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        vkuznets <vkuznets@redhat.com>,
        "brijesh.singh@amd.com" <brijesh.singh@amd.com>,
        "konrad.wilk@oracle.com" <konrad.wilk@oracle.com>,
        "hch@lst.de" <hch@lst.de>,
        "parri.andrea@gmail.com" <parri.andrea@gmail.com>,
        "dave.hansen@intel.com" <dave.hansen@intel.com>
References: <20211201160257.1003912-1-ltykernel@gmail.com>
 <20211201160257.1003912-4-ltykernel@gmail.com>
 <MWHPR21MB159390BE1B546A6F90FB1F18D76A9@MWHPR21MB1593.namprd21.prod.outlook.com>
From:   Tianyu Lan <ltykernel@gmail.com>
In-Reply-To: <MWHPR21MB159390BE1B546A6F90FB1F18D76A9@MWHPR21MB1593.namprd21.prod.outlook.com>
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On 12/4/2021 3:17 AM, Michael Kelley (LINUX) wrote:
>> +static void __init hyperv_iommu_swiotlb_init(void)
>> +{
>> +	unsigned long hyperv_io_tlb_size;
>> +	void *hyperv_io_tlb_start;
>> +
>> +	/*
>> +	 * Allocate Hyper-V swiotlb bounce buffer at early place
>> +	 * to reserve large contiguous memory.
>> +	 */
>> +	hyperv_io_tlb_size = swiotlb_size_or_default();
>> +	hyperv_io_tlb_start = memblock_alloc(hyperv_io_tlb_size, PAGE_SIZE);
>> +
>> +	if (!hyperv_io_tlb_start)
>> +		pr_warn("Fail to allocate Hyper-V swiotlb buffer.\n");
> In the error case, won't swiotlb_init_with_tlb() end up panic'ing when
> it tries to zero out the memory?   The only real choice here is to
> return immediately after printing the message, and not call
> swiotlb_init_with_tlb().
> 

Yes, agree. Will update.