linux-kernel - [PATCH v3 4/5] Drivers: hv: Ensure large page GPA mapping is PMD-aligned

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Message-ID: 
 <175942296740.128138.11164607006125062344.stgit@skinsburskii-cloud-desktop.internal.cloudapp.net>
Date: Thu, 02 Oct 2025 16:36:07 +0000
From: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
To: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
 decui@...rosoft.com
Cc: linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3 4/5] Drivers: hv: Ensure large page GPA mapping is
 PMD-aligned

With the upcoming introduction of movable pages, a region doesn't guarantee
always having large pages mapped. Both mapping on fault and unmapping
during PTE invalidation may not be 2M-aligned, while the hypervisor
requires both the GFN and page count to be 2M-aligned to use the large page
flag.

Update the logic for large page mapping in mshv_region_remap_pages() to
require both page_offset and page_count to be PMD-aligned.

Signed-off-by: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
---
 drivers/hv/mshv_root_main.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
index 8bf0b5af25802..9547833a04681 100644
--- a/drivers/hv/mshv_root_main.c
+++ b/drivers/hv/mshv_root_main.c
@@ -34,6 +34,8 @@
 #include "mshv.h"
 #include "mshv_root.h"
 
+#define VALUE_PMD_ALIGNED(c)			(!((c) & (PTRS_PER_PMD - 1)))
+
 MODULE_AUTHOR("Microsoft");
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("Microsoft Hyper-V root partition VMM interface /dev/mshv");
@@ -1100,7 +1102,9 @@ mshv_region_remap_pages(struct mshv_mem_region *region, u32 map_flags,
 	if (page_offset + page_count > region->nr_pages)
 		return -EINVAL;
 
-	if (region->flags.large_pages)
+	if (region->flags.large_pages &&
+	    VALUE_PMD_ALIGNED(page_offset) &&
+	    VALUE_PMD_ALIGNED(page_count))
 		map_flags |= HV_MAP_GPA_LARGE_PAGE;
 
 	/* ask the hypervisor to map guest ram */