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From: Robin Murphy <robin.murphy@arm.com>
To: Tianyu Lan <ltykernel@gmail.com>, Christoph Hellwig <hch@lst.de>,
	konrad.wilk@oracle.com
Cc: kys@microsoft.com, haiyangz@microsoft.com,
	sthemmin@microsoft.com, wei.liu@kernel.org, tglx@linutronix.de,
	mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com,
	arnd@arndb.de, akpm@linux-foundation.org,
	gregkh@linuxfoundation.org, m.szyprowski@samsung.com,
	joro@8bytes.org, will@kernel.org, davem@davemloft.net,
	kuba@kernel.org, jejb@linux.ibm.com, martin.petersen@oracle.com,
	Tianyu Lan <Tianyu.Lan@microsoft.com>,
	iommu@lists.linux-foundation.org, linux-arch@vger.kernel.org,
	linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, linux-scsi@vger.kernel.org,
	netdev@vger.kernel.org, vkuznets@redhat.com,
	thomas.lendacky@amd.com, brijesh.singh@amd.com,
	sunilmut@microsoft.com
Subject: Re: [Resend RFC PATCH V2 10/12] HV/IOMMU: Add Hyper-V dma ops support
Date: Wed, 12 May 2021 18:29:29 +0100
Message-ID: <4793ae97-5e29-4a45-d2b6-61c151322065@arm.com> (raw)
In-Reply-To: <a316af73-2c96-f307-6285-593597e05123@gmail.com>

On 2021-05-12 17:01, Tianyu Lan wrote:
> Hi Christoph and Konrad:
>       Current Swiotlb bounce buffer uses a pool for all devices. There
> is a high overhead to get or free bounce buffer during performance test.
> Swiotlb code now use a global spin lock to protect bounce buffer data.
> Several device queues try to acquire the spin lock and this introduce
> additional overhead.
> 
> For performance and security perspective, each devices should have a
> separate swiotlb bounce buffer pool and so this part needs to rework.
> I want to check this is right way to resolve performance issues with 
> swiotlb bounce buffer. If you have some other suggestions,welcome.

We're already well on the way to factoring out SWIOTLB to allow for just 
this sort of more flexible usage like per-device bounce pools - see here:

https://lore.kernel.org/linux-iommu/20210510095026.3477496-1-tientzu@chromium.org/T/#t

FWIW this looks to have an awful lot in common with what's going to be 
needed for Android's protected KVM and Arm's Confidential Compute 
Architecture, so we'll all be better off by doing it right. I'm getting 
the feeling that set_memory_decrypted() wants to grow into a more 
general abstraction that can return an alias at a different GPA if 
necessary.

Robin.

> 
> Thanks.
> 
> On 4/14/2021 11:47 PM, Christoph Hellwig wrote:
>>> +static dma_addr_t hyperv_map_page(struct device *dev, struct page 
>>> *page,
>>> +                  unsigned long offset, size_t size,
>>> +                  enum dma_data_direction dir,
>>> +                  unsigned long attrs)
>>> +{
>>> +    phys_addr_t map, phys = (page_to_pfn(page) << PAGE_SHIFT) + offset;
>>> +
>>> +    if (!hv_is_isolation_supported())
>>> +        return phys;
>>> +
>>> +    map = swiotlb_tbl_map_single(dev, phys, size, HV_HYP_PAGE_SIZE, 
>>> dir,
>>> +                     attrs);
>>> +    if (map == (phys_addr_t)DMA_MAPPING_ERROR)
>>> +        return DMA_MAPPING_ERROR;
>>> +
>>> +    return map;
>>> +}
>>
>> This largerly duplicates what dma-direct + swiotlb does.  Please use
>> force_dma_unencrypted to force bounce buffering and just use the generic
>> code.
>>
>>> +    if (hv_isolation_type_snp()) {
>>> +        ret = hv_set_mem_host_visibility(
>>> +                phys_to_virt(hyperv_io_tlb_start),
>>> +                hyperv_io_tlb_size,
>>> +                VMBUS_PAGE_VISIBLE_READ_WRITE);
>>> +        if (ret)
>>> +            panic("%s: Fail to mark Hyper-v swiotlb buffer visible 
>>> to host. err=%d\n",
>>> +                  __func__, ret);
>>> +
>>> +        hyperv_io_tlb_remap = ioremap_cache(hyperv_io_tlb_start
>>> +                        + ms_hyperv.shared_gpa_boundary,
>>> +                            hyperv_io_tlb_size);
>>> +        if (!hyperv_io_tlb_remap)
>>> +            panic("%s: Fail to remap io tlb.\n", __func__);
>>> +
>>> +        memset(hyperv_io_tlb_remap, 0x00, hyperv_io_tlb_size);
>>> +        swiotlb_set_bounce_remap(hyperv_io_tlb_remap);
>>
>> And this really needs to go into a common hook where we currently just
>> call set_memory_decrypted so that all the different schemes for these
>> trusted VMs (we have about half a dozen now) can share code rather than
>> reinventing it.
>>

  reply index

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-14 14:49 [Resend RFC PATCH V2 00/12] x86/Hyper-V: Add Hyper-V Isolation VM support Tianyu Lan
2021-04-14 14:49 ` [Resend RFC PATCH V2 01/12] x86/HV: Initialize GHCB page in Isolation VM Tianyu Lan
2021-04-14 14:49 ` [Resend RFC PATCH V2 02/12] x86/HV: Initialize shared memory boundary " Tianyu Lan
2021-04-14 14:49 ` [Resend RFC PATCH V2 03/12] x86/Hyper-V: Add new hvcall guest address host visibility support Tianyu Lan
2021-04-14 15:40   ` Christoph Hellwig
2021-04-15  8:13     ` Tianyu Lan
2021-04-14 14:49 ` [Resend RFC PATCH V2 04/12] HV: Add Write/Read MSR registers via ghcb Tianyu Lan
2021-04-14 15:41   ` Christoph Hellwig
2021-04-15  8:19     ` Tianyu Lan
2021-04-15 18:11   ` Konrad Rzeszutek Wilk
2021-04-14 14:49 ` [Resend RFC PATCH V2 05/12] HV: Add ghcb hvcall support for SNP VM Tianyu Lan
2021-04-14 14:49 ` [Resend RFC PATCH V2 06/12] HV/Vmbus: Add SNP support for VMbus channel initiate message Tianyu Lan
2021-04-15 18:52   ` Konrad Rzeszutek Wilk
2021-04-14 14:49 ` [Resend RFC PATCH V2 07/12] HV/Vmbus: Initialize VMbus ring buffer for Isolation VM Tianyu Lan
2021-04-15 20:24   ` Konrad Rzeszutek Wilk
2021-04-19  6:36     ` Christoph Hellwig
2021-04-14 14:49 ` [Resend RFC PATCH V2 08/12] UIO/Hyper-V: Not load UIO HV driver in the isolation VM Tianyu Lan
2021-04-14 15:42   ` Christoph Hellwig
2021-04-14 15:45   ` Greg KH
2021-04-14 16:17     ` Stephen Hemminger
2021-04-15 12:54       ` Tianyu Lan
2021-04-15 13:09     ` Tianyu Lan
2021-04-14 14:49 ` [Resend RFC PATCH V2 09/12] swiotlb: Add bounce buffer remap address setting function Tianyu Lan
2021-04-15 20:28   ` Konrad Rzeszutek Wilk
2021-04-14 14:49 ` [Resend RFC PATCH V2 10/12] HV/IOMMU: Add Hyper-V dma ops support Tianyu Lan
2021-04-14 15:47   ` Christoph Hellwig
2021-05-12 16:01     ` Tianyu Lan
2021-05-12 17:29       ` Robin Murphy [this message]
2021-05-13  3:19       ` Lu Baolu
2021-04-14 14:49 ` [Resend RFC PATCH V2 11/12] HV/Netvsc: Add Isolation VM support for netvsc driver Tianyu Lan
2021-04-14 15:50   ` Christoph Hellwig
2021-04-15  8:39     ` Tianyu Lan
2021-04-14 14:49 ` [Resend RFC PATCH V2 12/12] HV/Storvsc: Add Isolation VM support for storvsc driver Tianyu Lan
2021-04-14 15:51   ` Christoph Hellwig

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