> Subject: [EXTERNAL] RE: [PATCH 1/2] Drivers: hv: Allocate interrupt and
> monitor
> pages aligned to system page boundary
>
> From: lon...@linuxonhyperv.com <lon...@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: sta...@vger.kernel.org
> > Fixes: ca48739e59df ("Drivers: hv: vmbus: Move Hyper-V page allocator
> > to arch neutral
> > code")
> > Signed-off-by: Long Li <lon...@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
> >
