Re: linux-next: build warnings after merge of the kvm-arm-fixes tree

[Oliver Upton]

On Tue, Jul 07, 2026 at 02:17:20PM +0100, Marc Zyngier wrote:
> On Tue, 07 Jul 2026 13:11:55 +0100,
> Mark Brown <broonie@xxxxxxxxxx> wrote:
> > 
> > Hi all,
> > 
> > After merging the kvm-arm-fixes tree, today's linux-next build
> > (arm64 defconfig) started generating warnings:
> > 
> > In file included from /tmp/next/build/include/linux/limits.h:7,
> >                  from /tmp/next/build/include/linux/overflow.h:6,
> >                  from /tmp/next/build/include/linux/bits.h:32,
> >                  from /tmp/next/build/arch/arm64/include/asm/kvm_pgtable.h:10,
> >                  from /tmp/next/build/arch/arm64/kvm/hyp/pgtable.c:11:
> > /tmp/next/build/arch/arm64/kvm/hyp/pgtable.c: In function 'kvm_pgtable_stage2_relax_perms':
> > /tmp/next/build/include/vdso/limits.h:8:25: warning: overflow in conversion from 'int' to 's8' {aka 'signed char'} changes value from '2147483647' to '-1' [-Woverflow]
> >     8 | #define INT_MAX         ((int)(~0U >> 1))
> >       |                         ^
> > /tmp/next/build/arch/arm64/include/asm/tlbflush.h:131:33: note: in expansion of macro 'INT_MAX'
> >   131 | #define TLBI_TTL_UNKNOWN        INT_MAX
> >       |                                 ^~~~~~~
> > /tmp/next/build/arch/arm64/kvm/hyp/pgtable.c:1361:20: note: in expansion of macro 'TLBI_TTL_UNKNOWN'
> >  1361 |         s8 level = TLBI_TTL_UNKNOWN;
> >       |                    ^~~~~~~~~~~~~~~~
> > In file included from /tmp/next/build/include/linux/limits.h:7,
> >                  from /tmp/next/build/include/linux/overflow.h:6,
> >                  from /tmp/next/build/include/linux/bits.h:32,
> >                  from /tmp/next/build/arch/arm64/include/asm/kvm_pgtable.h:10,
> >                  from /tmp/next/build/arch/arm64/kvm/hyp/nvhe/../pgtable.c:11:
> > /tmp/next/build/arch/arm64/kvm/hyp/nvhe/../pgtable.c: In function 'kvm_pgtable_stage2_relax_perms':
> > /tmp/next/build/include/vdso/limits.h:8:25: warning: overflow in conversion from 'int' to 's8' {aka 'signed char'} changes value from '2147483647' to '-1' [-Woverflow]
> >     8 | #define INT_MAX         ((int)(~0U >> 1))
> >       |                         ^
> > /tmp/next/build/arch/arm64/include/asm/tlbflush.h:131:33: note: in expansion of macro 'INT_MAX'
> >   131 | #define TLBI_TTL_UNKNOWN        INT_MAX
> >       |                                 ^~~~~~~
> > /tmp/next/build/arch/arm64/kvm/hyp/nvhe/../pgtable.c:1361:20: note: in expansion of macro 'TLBI_TTL_UNKNOWN'
> >  1361 |         s8 level = TLBI_TTL_UNKNOWN;
> >       |                    ^~~~~~~~~~~~~~~~
> > 
> > 
> > Caused by commit
> > 
> >    100baf0184896 (KVM: arm64: Ensure level is always initialized when relaxing perms)
> > 
> > I imagine this will cause an allyesconfig build failure when I get to
> > that due to -Werror.
> 
> Crap, I don't know how I missed that one! And the whole thing is
> pretty dodgy anyway:
> 
> - level starts as s8
> - passed to __kvm_tlb_flush_vmid_ipa_nsh() as int
> - passed to __tlbi_level() as u32
> - compared to the value 3
> 
> The problem is that we are conflating the level of a descriptor and
> the TTL, which may or may not be related.
> 
> I'm minded to queue something like this on top. Oliver?
> 
> Thanks for the heads up,
> 
> 	M.
> 
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index 8754c99c22f2f..70dceb20dfada 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -1356,7 +1356,7 @@ int kvm_pgtable_stage2_relax_perms(struct kvm_pgtable *pgt, u64 addr,
>  				   enum kvm_pgtable_prot prot, enum kvm_pgtable_walk_flags flags)
>  {
>  	kvm_pte_t xn = 0, set = 0, clr = 0;
> -	s8 level = TLBI_TTL_UNKNOWN;
> +	s8 level;
>  	int ret;
>  
>  	if (prot & KVM_PTE_LEAF_ATTR_HI_SW)
> @@ -1379,7 +1379,8 @@ int kvm_pgtable_stage2_relax_perms(struct kvm_pgtable *pgt, u64 addr,
>  
>  	ret = stage2_update_leaf_attrs(pgt, addr, 1, set, clr, NULL, &level, flags);
>  	if (!ret || ret == -EAGAIN)
> -		kvm_call_hyp(__kvm_tlb_flush_vmid_ipa_nsh, pgt->mmu, addr, level);
> +		kvm_call_hyp(__kvm_tlb_flush_vmid_ipa_nsh, pgt->mmu, addr,
> +			     (ret == -EAGAIN) ? TLBI_TTL_UNKNOWN : level);

Looks good, sorry for the mess.

Reviewed-by: Oliver Upton <oupton@xxxxxxxxxx>

Thanks,
Oliver