linux-kernel - Re: [RFC PATCH V3 10/11] HV/Netvsc: Add Isolation VM support for netvsc driver

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Message-ID: <279cb4bf-c5b6-6db9-0f1e-9238e902c8f2@gmail.com>
Date:   Mon, 7 Jun 2021 23:21:20 +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, x86@...nel.org, hpa@...or.com,
        arnd@...db.de, dave.hansen@...ux.intel.com, luto@...nel.org,
        peterz@...radead.org, akpm@...ux-foundation.org,
        kirill.shutemov@...ux.intel.com, rppt@...nel.org,
        hannes@...xchg.org, cai@....pw, krish.sadhukhan@...cle.com,
        saravanand@...com, Tianyu.Lan@...rosoft.com,
        konrad.wilk@...cle.com, m.szyprowski@...sung.com,
        robin.murphy@....com, boris.ostrovsky@...cle.com, jgross@...e.com,
        sstabellini@...nel.org, joro@...tes.org, will@...nel.org,
        xen-devel@...ts.xenproject.org, davem@...emloft.net,
        kuba@...nel.org, jejb@...ux.ibm.com, martin.petersen@...cle.com,
        iommu@...ts.linux-foundation.org, linux-arch@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, netdev@...r.kernel.org,
        vkuznets@...hat.com, thomas.lendacky@....com,
        brijesh.singh@....com, sunilmut@...rosoft.com
Subject: Re: [RFC PATCH V3 10/11] HV/Netvsc: Add Isolation VM support for
 netvsc driver



On 6/7/2021 2:50 PM, Christoph Hellwig wrote:
> On Sun, May 30, 2021 at 11:06:27AM -0400, Tianyu Lan wrote:
>> +	if (hv_isolation_type_snp()) {
>> +		pfns = kcalloc(buf_size / HV_HYP_PAGE_SIZE, sizeof(unsigned long),
>> +			       GFP_KERNEL);
>> +		for (i = 0; i < buf_size / HV_HYP_PAGE_SIZE; i++)
>> +			pfns[i] = virt_to_hvpfn(net_device->recv_buf + i * HV_HYP_PAGE_SIZE) +
>> +				(ms_hyperv.shared_gpa_boundary >> HV_HYP_PAGE_SHIFT);
>> +
>> +		vaddr = vmap_pfn(pfns, buf_size / HV_HYP_PAGE_SIZE, PAGE_KERNEL_IO);
>> +		kfree(pfns);
>> +		if (!vaddr)
>> +			goto cleanup;
>> +		net_device->recv_original_buf = net_device->recv_buf;
>> +		net_device->recv_buf = vaddr;
>> +	}
> 
> This probably wnats a helper to make the thing more readable.  But who
> came up with this fucked up communication protocol where the host needs
> to map random pfns into a contigous range?  Sometime I really have to
> wonder what crack the hyper-v people take when comparing this to the
> relatively sane approach others take.

Agree. Will add a helper function.
> 
>> +	for (i = 0; i < page_count; i++)
>> +		dma_unmap_single(&hv_dev->device, packet->dma_range[i].dma,
>> +				 packet->dma_range[i].mapping_size,
>> +				 DMA_TO_DEVICE);
>> +
>> +	kfree(packet->dma_range);
> 
> Any reason this isn't simply using a struct scatterlist?

I will have a look. Thanks to reminder scatterlist.

> 
>> +	for (i = 0; i < page_count; i++) {
>> +		char *src = phys_to_virt((pb[i].pfn << HV_HYP_PAGE_SHIFT)
>> +					 + pb[i].offset);
>> +		u32 len = pb[i].len;
>> +
>> +		dma = dma_map_single(&hv_dev->device, src, len,
>> +				     DMA_TO_DEVICE);
> 
> dma_map_single can only be used on page baked memory, and if this is
> using page backed memory you wouldn't need to do thee phys_to_virt
> tricks.  Can someone explain the mess here in more detail?

Sorry. Could you elaborate the issue? These pages in the pb array are 
not allocated by DMA API and using dma_map_single() here is to map these 
pages' address to bounce buffer physical address.

> 
>>   	struct rndis_device *dev = nvdev->extension;
>>   	struct rndis_request *request = NULL;
>> +	struct hv_device *hv_dev = ((struct net_device_context *)
>> +			netdev_priv(ndev))->device_ctx;
> 
> Why not use a net_device_context local variable instead of this cast
> galore?
> 

OK. I will update.


Thanks.