Re: [PATCH 1/2] kvm: rework memory prefault

[Steffen Eiden <seiden@linux.ibm.com>]

On Tue, May 26, 2026 at 02:52:19PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> When both s390 and arm64 KVM modules are enabled on s390,
> the latter fails to link against the s390 version of
> kvm_arch_vcpu_pre_fault_memory():
> 
> ERROR: modpost: "kvm_arch_vcpu_pre_fault_memory" [arch/s390/kvm/arm64/kvm-arm64.ko] undefined!
> 
> Change the logic to reference this based on a target
> specific macro rather than a global Kconfig symbol.
> 
> Fixes: f67bba50ef56 ("KVM: s390: arm64: Enable KVM_ARM64 config and Kbuild")
> Fixes: 927ce4dee94f ("KVM: s390: Implement KVM_PRE_FAULT_MEMORY")
> 

Thanks for looking into this.

An alternative solution could be for the kvm-arm64 module to just implement the
function as well. The s390 implementation is purely gmap based and has no
dependencies to s390-kvm beside that. arm on s390 kvm could use the exact same
implementation as well. 

I guess this is probably dead code as (I assume) qemu-aarch64 does not use the feature.
But I saw some proposals regarding this feature for KVM/arm64 on the list.

> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> This is not yet an actual problem, but will be when both
> the experimental 'sae' branch and the 7.2 contents from
> current linux-next are merged.
> 
> Not sure who should carry this patch in the meantime, but
> it would be possible to add it to kvm-next already in
> preparation for the upcoming sae support.

I would prefer if you put it in next now. Less patches to carry around.

But If that is not feasible I can add it to series 1 once Claudios patches are
in 7.2.

	Steffen