linux-kernel - Re: [PATCH v7 05/12] KVM: guest_memfd: Add flag to remove from direct map

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Message-ID: <aQiJAfO8wiVPko_N@kernel.org>
Date: Mon, 3 Nov 2025 12:50:41 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Brendan Jackman <jackmanb@...gle.com>
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Subject: Re: [PATCH v7 05/12] KVM: guest_memfd: Add flag to remove from
 direct map

On Mon, Nov 03, 2025 at 10:35:38AM +0000, Brendan Jackman wrote:
> On Sat Nov 1, 2025 at 9:39 AM UTC, Mike Rapoport wrote:
> > On Fri, Oct 31, 2025 at 05:30:12PM +0000, Brendan Jackman wrote:
> >> On Wed Sep 24, 2025 at 3:22 PM UTC, Patrick Roy wrote:
> >> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> >> > index 1d0585616aa3..73a15cade54a 100644
> >> > --- a/include/linux/kvm_host.h
> >> > +++ b/include/linux/kvm_host.h
> >> > @@ -731,6 +731,12 @@ static inline bool kvm_arch_has_private_mem(struct kvm *kvm)
> >> >  bool kvm_arch_supports_gmem_mmap(struct kvm *kvm);
> >> >  #endif
> >> >  
> >> > +#ifdef CONFIG_KVM_GUEST_MEMFD
> >> > +#ifndef kvm_arch_gmem_supports_no_direct_map
> >> > +#define kvm_arch_gmem_supports_no_direct_map can_set_direct_map
> >> > +#endif
> >> > +#endif /* CONFIG_KVM_GUEST_MEMFD */
> >> 
> >> The test robot seems happy so I think I'm probably mistaken here, but
> >> AFAICS can_set_direct_map only exists when ARCH_HAS_SET_DIRECT_MAP,
> >> which powerpc doesn't set.
> >
> > We have stubs returning 0 for architectures that don't have
> > ARCH_HAS_SET_DIRECT_MAP.
> 
> I can't see any such stub for can_set_direct_map() specifically?

include/linux/set_memory.h:

#ifndef CONFIG_ARCH_HAS_SET_DIRECT_MAP
static inline int set_direct_map_invalid_noflush(struct page *page)
{
	return 0;
}
static inline int set_direct_map_default_noflush(struct page *page)
{
	return 0;
}

static inline int set_direct_map_valid_noflush(struct page *page,
					       unsigned nr, bool valid)
{
	return 0;
}

static inline bool kernel_page_present(struct page *page)
{
	return true;
}
#else /* CONFIG_ARCH_HAS_SET_DIRECT_MAP */
/*
 * Some architectures, e.g. ARM64 can disable direct map modifications at
 * boot time. Let them overrive this query.
 */
#ifndef can_set_direct_map
static inline bool can_set_direct_map(void)
{
	return true;
}
#define can_set_direct_map can_set_direct_map
#endif
#endif /* CONFIG_ARCH_HAS_SET_DIRECT_MAP */

 
> (But again, the bot seems happy, so I still suspect I'm wrong somehow or
> other).

-- 
Sincerely yours,
Mike.