From: longli@linuxonhyperv.com longli@linuxonhyperv.com Sent: Wednesday, April 30, 2025 3:06 PM

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

s/UIO, they/UIO, so they/

allocation APIs introduced earlier broke those requirements.

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

This patch modifies hv_alloc_hyperv_page() and friends. Then Patch 4 of the series deletes them, including the modifications. It would be less code motion to do the first part of Patch 4 (i.e., the use of __get_free_page directly in connection.c) here in Patch 1, and leave hv_alloc_hyperv_page() and friends unmodified. Continue to make the change to hv_kmsg_dump_register() here in Patch 1 as well.

Then have Patch 2 simply delete hv_alloc_hyperv_page() and friends because they are no longer used. The modifications to hv_alloc_hyperv_page() and friends would not be needed.

Patch 3 and 4 would be the additional changes in uio_hv_generic.c.

Michael

Cc: stable@vger.kernel.org Fixes: ca48739e59df ("Drivers: hv: vmbus: Move Hyper-V page allocator to arch neutral code") Signed-off-by: Long Li longli@microsoft.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