From: Long Li <[email protected]> Sent: Wednesday, April 23, 2025 11:40 AM > > > > > > 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 > > > > > 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: [email protected] > > > Fixes: ca48739e59df ("Drivers: hv: vmbus: Move Hyper-V page allocator > > > to arch neutral > > > code") > > > Signed-off-by: Long Li <[email protected]> > > > --- > > > 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 > > > >
