linux-kernel - [Patch v2 1/4] Drivers: hv: Allocate interrupt and monitor pages aligned to system page boundary

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Message-Id: <1746050758-6829-2-git-send-email-longli@linuxonhyperv.com>
Date: Wed, 30 Apr 2025 15:05:55 -0700
From: longli@...uxonhyperv.com
To: "K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>,
	Dexuan Cui <decui@...rosoft.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-hyperv@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Long Li <longli@...rosoft.com>,
	stable@...r.kernel.org
Subject: [Patch v2 1/4] Drivers: hv: Allocate interrupt and monitor pages aligned to system page boundary

From: Long Li <longli@...rosoft.com>

There are use cases that interrupt and monitor pages are mapped to
user-mode through UIO, they need to be system page aligned. Some Hyper-V
allocation APIs introduced earlier broke those requirements.

Fix those APIs by always allocating Hyper-V page at system page boundaries.

Cc: stable@...r.kernel.org
Fixes: ca48739e59df ("Drivers: hv: vmbus: Move Hyper-V page allocator to arch neutral code")
Signed-off-by: Long Li <longli@...rosoft.com>
---
 drivers/hv/hv_common.c | 35 ++++++++++-------------------------
 1 file changed, 10 insertions(+), 25 deletions(-)

diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
index a7d7494feaca..297ccd7d4997 100644
--- a/drivers/hv/hv_common.c
+++ b/drivers/hv/hv_common.c
@@ -106,41 +106,26 @@ void __init hv_common_free(void)
 }
 
 /*
- * Functions for allocating and freeing memory with size and
- * alignment HV_HYP_PAGE_SIZE. These functions are needed because
- * the guest page size may not be the same as the Hyper-V page
- * size. We depend upon kmalloc() aligning power-of-two size
- * allocations to the allocation size boundary, so that the
- * allocated memory appears to Hyper-V as a page of the size
- * it expects.
+ * A Hyper-V page can be used by UIO for mapping to user-space, it should
+ * always be allocated on system page boundaries.
  */
-
 void *hv_alloc_hyperv_page(void)
 {
-	BUILD_BUG_ON(PAGE_SIZE <  HV_HYP_PAGE_SIZE);
-
-	if (PAGE_SIZE == HV_HYP_PAGE_SIZE)
-		return (void *)__get_free_page(GFP_KERNEL);
-	else
-		return kmalloc(HV_HYP_PAGE_SIZE, GFP_KERNEL);
+	BUILD_BUG_ON(PAGE_SIZE < HV_HYP_PAGE_SIZE);
+	return (void *)__get_free_page(GFP_KERNEL);
 }
 EXPORT_SYMBOL_GPL(hv_alloc_hyperv_page);
 
 void *hv_alloc_hyperv_zeroed_page(void)
 {
-	if (PAGE_SIZE == HV_HYP_PAGE_SIZE)
-		return (void *)__get_free_page(GFP_KERNEL | __GFP_ZERO);
-	else
-		return kzalloc(HV_HYP_PAGE_SIZE, GFP_KERNEL);
+	BUILD_BUG_ON(PAGE_SIZE < HV_HYP_PAGE_SIZE);
+	return (void *)__get_free_page(GFP_KERNEL | __GFP_ZERO);
 }
 EXPORT_SYMBOL_GPL(hv_alloc_hyperv_zeroed_page);
 
 void hv_free_hyperv_page(void *addr)
 {
-	if (PAGE_SIZE == HV_HYP_PAGE_SIZE)
-		free_page((unsigned long)addr);
-	else
-		kfree(addr);
+	free_page((unsigned long)addr);
 }
 EXPORT_SYMBOL_GPL(hv_free_hyperv_page);
 
@@ -272,7 +257,7 @@ static void hv_kmsg_dump_unregister(void)
 	atomic_notifier_chain_unregister(&panic_notifier_list,
 					 &hyperv_panic_report_block);
 
-	hv_free_hyperv_page(hv_panic_page);
+	kfree(hv_panic_page);
 	hv_panic_page = NULL;
 }
 
@@ -280,7 +265,7 @@ static void hv_kmsg_dump_register(void)
 {
 	int ret;
 
-	hv_panic_page = hv_alloc_hyperv_zeroed_page();
+	hv_panic_page = kzalloc(HV_HYP_PAGE_SIZE, GFP_KERNEL);
 	if (!hv_panic_page) {
 		pr_err("Hyper-V: panic message page memory allocation failed\n");
 		return;
@@ -289,7 +274,7 @@ static void hv_kmsg_dump_register(void)
 	ret = kmsg_dump_register(&hv_kmsg_dumper);
 	if (ret) {
 		pr_err("Hyper-V: kmsg dump register error 0x%x\n", ret);
-		hv_free_hyperv_page(hv_panic_page);
+		kfree(hv_panic_page);
 		hv_panic_page = NULL;
 	}
 }
-- 
2.34.1