[PATCH 2/2] IB/hfi1: Fix the PIO_CRED credit-return mmap

[Shuhei Takeshita <jyohuku.alterego@gmail.com>]

hfi1_file_mmap()'s PIO_CRED case must hand user space the single
credit-return page that holds this context's entry.  That page is the
second or third page of the per-node credit-return allocation once the
hardware send context index reaches 64 or 128, so the failure below is
intermittent: when the entry lands on the first page the offset is zero
and everything works.

Two things are wrong.

First, cr_page_offset is a byte offset but .va is a struct
credit_return *, so adding it is pointer arithmetic and scales the offset
by sizeof(struct credit_return) == 64.  memvirt then lands 256 KiB or
512 KiB past a 10240-byte allocation.  With an IOMMU translating, that
address is inside the vmalloc range but in no vm_area, so
dma_mmap_coherent() -> iommu_dma_mmap() finds no pages, vmalloc_to_pfn()
returns page_to_pfn(NULL), and remap_pfn_range() installs a frame above
MAXPHYADDR.  The first user read then takes:

  psm2_ep_open_pr: Corrupted page table at address 7a14d007e000
  PGD 800000013886a067 P4D 800000013886a067 PUD 13886b067 PMD 13886c067
                                            PTE 800049168e911235
  Oops: Bad pagetable: 000d [#1] SMP PTI

Second, and still wrong once the arithmetic is corrected,
dma_mmap_coherent() describes a whole coherent buffer and selects the
page within it with vma->vm_pgoff.  Offsetting cpu_addr has no effect:
for a vmap'd allocation iommu_dma_mmap() uses cpu_addr only to locate the
vm_area and then maps pages[vm_pgoff], which hfi1_file_mmap() has just
set to 0.  User space therefore always receives the first credit-return
page, every credit read is for the wrong context, and send PIO stalls
forever.

Use the DMA API as intended: pass the base of the allocation with its
full length and select the page with vm_pgoff.  A separate length is
needed because memlen must keep describing the VMA for the existing size
check.  The dma-direct path stays correct as well, since dma_direct_mmap()
adds the same vm_pgoff to the base pfn.

Tested on a Dell T7610 (Xeon E5-2650 v2, Intel IOMMU in DMA-FQ mode)
against a Threadripper PRO 3995WX peer, both Omni-Path 100.  Before this
change psm2_ep_open() Oopses the kernel; with only the arithmetic
corrected psm2_ep_open() succeeds but any transfer that uses send PIO
hangs, PSM2_SDMA=2 (send PIO disabled) completing normally while
PSM2_SDMA=0 (send PIO only) hangs every time.  With this change send PIO,
send DMA and the default mixed mode all work.

Fixes: 1ec82317a1da ("IB/hfi1: Use dma_mmap_coherent for matching buffers")
Cc: stable@vger.kernel.org
Signed-off-by: Shuhei Takeshita <jyohuku.alterego@gmail.com>
---
 drivers/infiniband/hw/hfi1/file_ops.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/drivers/infiniband/hw/hfi1/file_ops.c b/drivers/infiniband/hw/hfi1/file_ops.c
index e05f3c255..ad2044d1f 100644
--- a/drivers/infiniband/hw/hfi1/file_ops.c
+++ b/drivers/infiniband/hw/hfi1/file_ops.c
@@ -326,6 +326,7 @@ static int hfi1_file_mmap(struct file *fp, struct vm_area_struct *vma)
 	void *memvirt = NULL;
 	dma_addr_t memdma = 0;
 	u8 subctxt, mapio = 0, vmf = 0, type;
+	size_t memdmalen = 0;
 	ssize_t memlen = 0;
 	int ret = 0;
 	u16 ctxt;
@@ -371,7 +372,9 @@ static int hfi1_file_mmap(struct file *fp, struct vm_area_struct *vma)
 		mapio = 1;
 		break;
 	case PIO_CRED: {
+		struct credit_return_base *cr = &dd->cr_base[uctxt->sc->node];
 		u64 cr_page_offset;
+
 		if (flags & VM_WRITE) {
 			ret = -EPERM;
 			goto done;
@@ -381,11 +384,18 @@ static int hfi1_file_mmap(struct file *fp, struct vm_area_struct *vma)
 		 * second or third page allocated for credit returns (if number
 		 * of enabled contexts > 64 and 128 respectively).
 		 */
-		cr_page_offset = ((u64)uctxt->sc->hw_free -
-				  (u64)dd->cr_base[uctxt->sc->node].va) &
+		cr_page_offset = ((u64)uctxt->sc->hw_free - (u64)cr->va) &
 				 PAGE_MASK;
-		memvirt = dd->cr_base[uctxt->sc->node].va + cr_page_offset;
-		memdma = dd->cr_base[uctxt->sc->node].dma + cr_page_offset;
+		/*
+		 * dma_mmap_coherent() describes the whole coherent buffer and
+		 * selects the page within it with vma->vm_pgoff, so pass the
+		 * base of the allocation and its length and let vm_pgoff pick
+		 * the page.
+		 */
+		vma->vm_pgoff = cr_page_offset >> PAGE_SHIFT;
+		memvirt = cr->va;
+		memdma = cr->dma;
+		memdmalen = TXE_NUM_CONTEXTS * sizeof(struct credit_return);
 		memlen = PAGE_SIZE;
 		flags &= ~VM_MAYWRITE;
 		flags |= VM_DONTCOPY | VM_DONTEXPAND;
@@ -567,7 +577,8 @@ static int hfi1_file_mmap(struct file *fp, struct vm_area_struct *vma)
 		ret = 0;
 	} else if (memdma) {
 		ret = dma_mmap_coherent(&dd->pcidev->dev, vma,
-					memvirt, memdma, memlen);
+					memvirt, memdma,
+					memdmalen ? memdmalen : memlen);
 	} else if (mapio) {
 		ret = io_remap_pfn_range(vma, vma->vm_start,
 					 PFN_DOWN(memaddr),
-- 
2.43.0