Re: [PATCH v6 04/10] arm64: hyperv: Add memory alloc/free functions for Hyper-V size pages

[Arnd Bergmann <arnd@arndb.de>]

On Sat, Mar 14, 2020 at 4:36 PM Michael Kelley <mikelley@microsoft.com> wrote:
>  /*
> + * 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.
> + *
> + * These functions are used by arm64 specific code as well as
> + * arch independent Hyper-V drivers.
> + */
> +
> +void *hv_alloc_hyperv_page(void)
> +{
> +       BUILD_BUG_ON(PAGE_SIZE <  HV_HYP_PAGE_SIZE);
> +       return kmalloc(HV_HYP_PAGE_SIZE, GFP_KERNEL);
> +}
> +EXPORT_SYMBOL_GPL(hv_alloc_hyperv_page);

I don't think there is any guarantee that kmalloc() returns page-aligned
allocations in general. How about using get_free_pages()
to implement this?

       Arnd