Re: [PATCH v8 3/9] Documentation/x86: Add documentation for SVA (Shared Virtual Addressing)

From: Borislav Petkov
Date: Thu Sep 17 2020 - 03:56:16 EST

On Tue, Sep 15, 2020 at 09:30:07AM -0700, Fenghua Yu wrote:
> +Background
> +==========
> +
> +Shared Virtual Addressing (SVA) allows the processor and device to use the
> +same virtual addresses avoiding the need for software to translate virtual
> +addresses to physical addresses. SVA is what PCIe calls Shared Virtual
> +Memory (SVM).
> +
> +In addition to the convenience of using application virtual addresses
> +by the device, it also doesn't require pinning pages for DMA.
> +PCIe Address Translation Services (ATS) along with Page Request Interface
> +(PRI) allow devices to function much the same way as the CPU handling
> +application page-faults. For more information please refer to the PCIe
> +specification Chapter 10: ATS Specification.
> +
> +Use of SVA requires IOMMU support in the platform. IOMMU also is required
> +to support PCIe features ATS and PRI. ATS allows devices to cache
> +translations for virtual addresses. The IOMMU driver uses the mmu_notifier()
> +support to keep the device TLB cache and the CPU cache in sync. PRI allows
> +the device to request paging the virtual address by using the CPU page tables
> +before accessing the address.

That still reads funny, the "the device to request paging the virtual
address" part. Do you mean that per chance here:

"Before the device can access that address, the device uses the PRI in
order to request the virtual address to be paged in into the CPU page