From: Vitaly Kuznetsov <vkuzn...@redhat.com> Sent: Tuesday, March 2, 2021 4:57
AM
>
> Michael Kelley <mikel...@microsoft.com> writes:
>
> > The Hyper-V page allocator functions are implemented in an architecture
> > neutral way. Move them into the architecture neutral VMbus module so
> > a separate implementation for ARM64 is not needed.
> >
> > No functional change.
> >
> > Signed-off-by: Michael Kelley <mikel...@microsoft.com>
> > Reviewed-by: Boqun Feng <boqun.f...@gmail.com>
> > ---
> > arch/x86/hyperv/hv_init.c | 22 ----------------------
> > arch/x86/include/asm/mshyperv.h | 5 -----
> > drivers/hv/hv.c | 36 ++++++++++++++++++++++++++++++++++++
> > include/asm-generic/mshyperv.h | 4 ++++
> > 4 files changed, 40 insertions(+), 27 deletions(-)
> >
[snip]
> >
> > /*
> > + * 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.
> > + */
> > +
> > +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);
>
> PAGE_SIZE and HV_HYP_PAGE_SIZE are known compile-time and in case this
> won't change in the future we can probably write this as
>
> #if PAGE_SIZE == HV_HYP_PAGE_SIZE
> return (void *)__get_free_page(GFP_KERNEL);
> #else
> return kmalloc(HV_HYP_PAGE_SIZE, GFP_KERNEL);
> #endif
>
> (not sure if the output is going to be any different with e.g. gcc's '-O2')
>
I looked at the generated code, and the compiler does the right
thing on both x86/x64 and on ARM64. I'd rather leave the code
as is so that both legs of the 'if' statement get checked by the
compiler regardless of whether PAGE_SIZE == HV_HYP_PAGE_SIZE.
Michael
> > +}
> > +
> > +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);
> > +}
> > +
> > +void hv_free_hyperv_page(unsigned long addr)
> > +{
> > + if (PAGE_SIZE == HV_HYP_PAGE_SIZE)
> > + free_page(addr);
> > + else
> > + kfree((void *)addr);
> > +}
> > +
> > +/*
