Subject: [EXTERNAL] RE: [PATCH 1/2] Drivers: hv: Allocate interrupt and monitor pages aligned to system page boundary
From: longli@linuxonhyperv.com longli@linuxonhyperv.com Sent: Thursday, April 17, 2025 5:43 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 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.
If there is no objection, I can remove these functions.
Long
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
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
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 | 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