linux-kernel - [PATCH v4 3/5] Drivers: hv: Batch GPA unmap operations to improve large region performance

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: 
 <175976318688.16834.16198650808431263017.stgit@skinsburskii-cloud-desktop.internal.cloudapp.net>
Date: Mon, 06 Oct 2025 15:06:26 +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 v4 3/5] Drivers: hv: Batch GPA unmap operations to improve
 large region performance

Reduce overhead when unmapping large memory regions by batching GPA unmap
operations in 2MB-aligned chunks.

Use a dedicated constant for batch size to improve code clarity and
maintainability.

Signed-off-by: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
---
 drivers/hv/mshv_root.h         |    2 ++
 drivers/hv/mshv_root_hv_call.c |    2 +-
 drivers/hv/mshv_root_main.c    |   28 +++++++++++++++++++++++++---
 3 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/drivers/hv/mshv_root.h b/drivers/hv/mshv_root.h
index e3931b0f12693..97e64d5341b6e 100644
--- a/drivers/hv/mshv_root.h
+++ b/drivers/hv/mshv_root.h
@@ -32,6 +32,8 @@ static_assert(HV_HYP_PAGE_SIZE == MSHV_HV_PAGE_SIZE);
 
 #define MSHV_PIN_PAGES_BATCH_SIZE	(0x10000000ULL / HV_HYP_PAGE_SIZE)
 
+#define MSHV_MAX_UNMAP_GPA_PAGES	512
+
 struct mshv_vp {
 	u32 vp_index;
 	struct mshv_partition *vp_partition;
diff --git a/drivers/hv/mshv_root_hv_call.c b/drivers/hv/mshv_root_hv_call.c
index c9c274f29c3c6..0696024ccfe31 100644
--- a/drivers/hv/mshv_root_hv_call.c
+++ b/drivers/hv/mshv_root_hv_call.c
@@ -17,7 +17,7 @@
 /* Determined empirically */
 #define HV_INIT_PARTITION_DEPOSIT_PAGES 208
 #define HV_MAP_GPA_DEPOSIT_PAGES	256
-#define HV_UMAP_GPA_PAGES		512
+#define HV_UMAP_GPA_PAGES		MSHV_MAX_UNMAP_GPA_PAGES
 
 #define HV_PAGE_COUNT_2M_ALIGNED(pg_count) (!((pg_count) & (0x200 - 1)))
 
diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
index 97e322f3c6b5e..b61bef6b9c132 100644
--- a/drivers/hv/mshv_root_main.c
+++ b/drivers/hv/mshv_root_main.c
@@ -1378,6 +1378,7 @@ mshv_map_user_memory(struct mshv_partition *partition,
 static void mshv_partition_destroy_region(struct mshv_mem_region *region)
 {
 	struct mshv_partition *partition = region->partition;
+	u64 gfn, gfn_count, start_gfn, end_gfn;
 	u32 unmap_flags = 0;
 	int ret;
 
@@ -1396,9 +1397,30 @@ static void mshv_partition_destroy_region(struct mshv_mem_region *region)
 	if (region->flags.large_pages)
 		unmap_flags |= HV_UNMAP_GPA_LARGE_PAGE;
 
-	/* ignore unmap failures and continue as process may be exiting */
-	hv_call_unmap_gpa_pages(partition->pt_id, region->start_gfn,
-				region->nr_pages, unmap_flags);
+	start_gfn = region->start_gfn;
+	end_gfn = region->start_gfn + region->nr_pages;
+
+	for (gfn = start_gfn; gfn < end_gfn; gfn += gfn_count) {
+		if (gfn % MSHV_MAX_UNMAP_GPA_PAGES)
+			gfn_count = ALIGN(gfn, MSHV_MAX_UNMAP_GPA_PAGES) - gfn;
+		else
+			gfn_count = MSHV_MAX_UNMAP_GPA_PAGES;
+
+		if (gfn + gfn_count > end_gfn)
+			gfn_count = end_gfn - gfn;
+
+		/* Skip if all pages in this range if none is mapped */
+		if (!memchr_inv(region->pages + (gfn - start_gfn), 0,
+				gfn_count * sizeof(struct page *)))
+			continue;
+
+		ret = hv_call_unmap_gpa_pages(partition->pt_id, gfn,
+					      gfn_count, unmap_flags);
+		if (ret)
+			pt_err(partition,
+			       "Failed to unmap GPA pages %#llx-%#llx: %d\n",
+			       gfn, gfn + gfn_count - 1, ret);
+	}
 
 	mshv_region_invalidate(region);