From: Long Li longli@microsoft.com Sent: Wednesday, April 23, 2025 11:40 AM

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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.

I'd suggest doing away with the hv_alloc/free_*() functions entirely since they are now reduced to just being a wrapper around __get_free_pages(), which doesn't add any value. Once all the arm64 support and CoCo VM code settled out, it turned out that these functions to allocate Hyper-V size pages had dwindling usage.

There is a BUILD_BUG_ON(PAGE_SIZE < HV_HYP_PAGE_SIZE) in those functions, but it probably doesn't do anything.

You could move the BUILD_BUG_ON() to vmbus_connection() where one of the calls to __get_free_pages() is made. That would codify the assumption that __get_free_pages() returns memory at least as large as HV_HYP_PAGE_SIZE.

Michael

If there is no objection, I can remove these functions.

Long

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Allocation of the interrupt and monitor pages can use __get_free_pages() directly, and that properly captures the need for those allocations to be a full page. Just add a comment that this wastes space when PAGE_SIZE

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HV_HYP_PAGE_SIZE, but is necessary because the page may be mapped

into user space by uio_hv_generic.

The only other use is in hv_kmsg_dump_register(), and it can do kzalloc(HV_HYP_PAGE_SIZE), since that case really is tied to the Hyper-V page size, not PAGE_SIZE. There's no need to waste space by allocating a full page.

Michael

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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

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drivers/hv/hv_common.c | 29 +++++++---------------------- 1 file changed, 7 insertions(+), 22 deletions(-)

diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c index a7d7494feaca..f426aaa9b8f9 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);

-- 2.34.1