RE: [RFC PATCH 2/2] hv_netvsc: back GPADL buffers with kmalloc + decrypt + vmap

["Kameron Carr" <kameroncarr@linux.microsoft.com>]

On Saturday, August 1, 2026 9:17 PM, Michael Kelley wrote:
> From: Kameron Carr <kameroncarr@linux.microsoft.com> Sent: Friday, July
31, 2026 12:06 PM
> >
> > On Friday, July 24, 2026 12:37 PM, Michael Kelley wrote:
> > > From: Kameron Carr <kameroncarr@linux.microsoft.com> Sent: Tuesday,
July 21, 2026 12:57 PM
> > [...]
> > > > +	/*
> > > > +	 * @order monotonically decreases across iterations
> > > > +	 *
> > > > +	 * Use __GFP_NORETRY | __GFP_NOWARN to avoid OOM-killing,
but try
> > > > +	 * harder at order 0 since that is the final fallback.
> > > > +	 */
> > > > +	order = min_t(unsigned int, MAX_PAGE_ORDER,
ilog2(nr_pages));
> > >
> > > Prefer using min() instead of min_t(). For normal integer values,
> > > min() should work correctly.
> >
> > Using min() compiled fine on ARM, but x86 is throwing a compile error.
> >
> >     drivers/hv/channel.c: In function 'vmbus_alloc_buffer':
> >     ././include/linux/compiler_types.h:699:45: error: call to
> >     '__compiletime_assert_518' declared with attribute error: min(order,
(
> >     __builtin_constant_p(remaining) ? ((remaining) < 2 ? 0 : 63 -
> >     __builtin_clzll(remaining)) : (sizeof(remaining) <= 4) ?
> >     __ilog2_u32(remaining) : __ilog2_u64(remaining) )) signedness error
> >
> > In my v3 I may go back to using min_t. Please let me know if a cast (or
> > some other method) is preferred.
> 
> Hmmm. I don't get the same compile error on x86/x64. Maybe it is
> related to compiler and version, or the kernel code base against which
> the patch is being built. Probably you didn't see a problem on arm64
> because of some such difference. FWIW, I built with gcc 11.4.0 against
> linux-next20260726.  What is the compiler and base kernel info where
> you saw the error and on arm64 where you didn't?

In both cases, I built against hyperv-next (a4ffc59).
On ARM64 I used gcc 13.2.0; on x86 I used 13.3.0.

To do a fair comparison, I
 * downgraded my x86 environment to gcc 13.2.0
 * started with `make defconfig`
 * enabled Hyper-V and NetVSC in the config (=y)

I saw the same behavior where there was no error on ARM and compile failure
on x86.

Regards,
Kameron