kpatch-build: add arm64 KVM to known deep finds

[jexbow]

On arm64, the KVM generic objects are built from arch/arm64/kvm/Makefile
with KVM=../../../virt/kvm, so kpatch-build has to resolve the object
name arch/arm64/kvm/../../../virt/kvm/kvm_main.o, whose parent is
arch/arm64/kvm/kvm.o.

find_parent_obj() already has a "prevent known deep finds" shortcut for
arch/x86/kvm, which covers the same situation on x86 (see #735), but
there is no arm64 counterpart. Patching a function in
virt/kvm/kvm_main.c therefore falls through to the full-tree deep find,
which fails to resolve the parent:

doing "deep find" for parent object
ERROR: invalid ancestor arch/arm64/kvm/../../../virt/kvm/kvm_main.o for arch/arm64/kvm/../../../virt/kvm/kvm_main.o

Add the corresponding shortcut for arch/arm64/kvm.

Tested on aarch64 with a 4.19 kernel and gcc 8.2.

[joe-lawrence]

Hi @jexbow : I don't see a change/MR attached to this issue, but would we need the same for all arches?

$ ls -ld arch/*/kvm
drwxr-xr-x. 1 jolawren jolawren  720 Aug 17 12:55 arch/arm64/kvm          <-
drwxr-xr-x. 1 jolawren jolawren  182 Jul 13 18:59 arch/loongarch/kvm      <-
drwxr-xr-x. 1 jolawren jolawren  240 Apr  8 21:49 arch/mips/kvm
drwxr-xr-x. 1 jolawren jolawren 2058 Jul 13 18:59 arch/powerpc/kvm        <-
drwxr-xr-x. 1 jolawren jolawren  732 Aug 17 12:55 arch/riscv/kvm
drwxr-xr-x. 1 jolawren jolawren  364 Aug 17 12:55 arch/s390/kvm           <-
drwxr-xr-x. 1 jolawren jolawren 2058 Aug 17 12:55 arch/x86/kvm            <-

[jexbow]

Hi @joe-lawrence, thanks for taking a look.

You're right on both counts:

1. No PR yet — I'll follow up with a code change shortly.
2. All arches — agreed, the fix shouldn't be arm64-specific. The existing shortcut hardcodes arch/x86/kvm, which only works when the target arch is x86. Instead of adding per-arch if blocks, I'll make it derive the correct arch/<arch>/kvm directory from $TARGET_ARCH (with a small mapping since the kpatch TARGET_ARCH values don't always match the kernel arch directory names, e.g. x86_64→x86, aarch64→arm64, ppc64le→powerpc, s390x→s390).

I've verified that on v4.19, arm64/x86/s390/powerpc all use the KVM=../../../virt/kvm pattern in their KVM Makefiles, and on modern kernels virt/kvm/Makefile.kvm still sets KVM ?= ../../../virt/kvm, so the issue applies to all of them. loongarch (added later) follows the same pattern on current kernels.

I only have arm64 hardware to test with (4.19 kernel, gcc 8.2), but the change is mechanical and the mapping covers all kpatch-supported arches.

Will send the PR soon.