Messages in this thread | | | Date | Mon, 16 Mar 2020 08:30:42 +0000 | From | Marc Zyngier <> | Subject | Re: [PATCH v6 04/10] arm64: hyperv: Add memory alloc/free functions for Hyper-V size pages |
| |
On 2020-03-16 08:22, Arnd Bergmann wrote: > 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.
I believe that guarantee came with 59bb47985c1db ("mm, sl[aou]b: guarantee natural alignment for kmalloc(power-of-two)").
> How about using get_free_pages() to implement this?
This would certainly work, at the expense of a lot of wasted memory when PAGE_SIZE isn't 4k.
Thanks,
M. -- Jazz is not dead. It just smells funny...
| |