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Commit 58629c0d authored by Alexey Kardashevskiy's avatar Alexey Kardashevskiy Committed by Michael Ellerman
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powerpc/powernv/npu: Fault user page into the hypervisor's pagetable 



When a page fault happens in a GPU, the GPU signals the OS and the GPU
driver calls the fault handler which populated a page table; this allows
the GPU to complete an ATS request.

On the bare metal get_user_pages() is enough as it adds a pte to
the kernel page table but under KVM the partition scope tree does not get
updated so ATS will still fail.

This reads a byte from an effective address which causes HV storage
interrupt and KVM updates the partition scope tree.

Signed-off-by: default avatarAlexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 135ef954

arch/powerpc/platforms/powernv/npu-dma.c

+7 −6
Original line number Diff line number Diff line
@@ -1132,6 +1132,8 @@ int pnv_npu2_handle_fault(struct npu_context *context, uintptr_t *ea, 
	u64 rc = 0, result = 0;

	int i, is_write;

	struct page *page[1];

	const char __user *u;

	char c;



	/* mmap_sem should be held so the struct_mm must be present */

	struct mm_struct *mm = context->mm;
@@ -1144,18 +1146,17 @@ int pnv_npu2_handle_fault(struct npu_context *context, uintptr_t *ea, 
					is_write ? FOLL_WRITE : 0,

					page, NULL, NULL);



		/*

		 * To support virtualised environments we will have to do an

		 * access to the page to ensure it gets faulted into the

		 * hypervisor. For the moment virtualisation is not supported in

		 * other areas so leave the access out.

		 */

		if (rc != 1) {

			status[i] = rc;

			result = -EFAULT;

			continue;

		}



		/* Make sure partition scoped tree gets a pte */

		u = page_address(page[0]);

		if (__get_user(c, u))

			result = -EFAULT;



		status[i] = 0;

		put_page(page[0]);

	}