linux-kernel - [PATCH v2] Convert backwards goto with a while loop

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Message-ID: <20230103194948.1806373-1-shacharr@google.com>
Date:   Tue,  3 Jan 2023 19:49:48 +0000
From:   Shachar Raindel <shacharr@...gle.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Shachar Raindel <shacharr@...gle.com>
Subject: [PATCH v2] Convert backwards goto with a while loop

The function vaddr_get_pfns used a goto retry structure to implement
retrying.  This is a gray area in the coding style guide (which is
only explicitly recommending goto for handling function exits).
Convert the code to a while loop, making it explicit that the
following block only runs when the pin attempt failed.

Signed-off-by: Shachar Raindel <shacharr@...gle.com>
---

Changelog:

v1 -> v2: Refine commit message, fix minor code style issue

 drivers/vfio/vfio_iommu_type1.c | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 23c24fe98c00..6335eabe1b7c 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -570,27 +570,28 @@ static int vaddr_get_pfns(struct mm_struct *mm, unsigned long vaddr,
 		}
 
 		*pfn = page_to_pfn(pages[0]);
-		goto done;
-	}
+	} else {
+		do {
+
+			/* This is not a normal page, lookup PFN for P2P DMA */
+			vaddr = untagged_addr(vaddr);
 
-	vaddr = untagged_addr(vaddr);
+			vma = vma_lookup(mm, vaddr);
 
-retry:
-	vma = vma_lookup(mm, vaddr);
+			if (!vma || !(vma->vm_flags & VM_PFNMAP))
+				break;
 
-	if (vma && vma->vm_flags & VM_PFNMAP) {
-		ret = follow_fault_pfn(vma, mm, vaddr, pfn, prot & IOMMU_WRITE);
-		if (ret == -EAGAIN)
-			goto retry;
+			ret = follow_fault_pfn(vma, mm, vaddr, pfn,
+					       prot & IOMMU_WRITE);
+			if (ret)
+				continue; /* Retry for EAGAIN, otherwise bail */
 
-		if (!ret) {
 			if (is_invalid_reserved_pfn(*pfn))
 				ret = 1;
 			else
 				ret = -EFAULT;
-		}
-	}
-done:
+		} while (ret == -EAGAIN);
+	}
 	mmap_read_unlock(mm);
 	return ret;
 }
-- 
2.39.0.314.g84b9a713c41-goog