powerpc: Fix is_kvm_guest() / kvm_para_available()

Commit a21d1becaa3f ("powerpc: Reintroduce is_kvm_guest() as a fast-path
check") added is_kvm_guest() and changed kvm_para_available() to use it.

is_kvm_guest() checks a static key, kvm_guest, and that static key is
set in check_kvm_guest().

The problem is check_kvm_guest() is only called on pseries, and even
then only in some configurations. That means is_kvm_guest() always
returns false on all non-pseries and some pseries depending on
configuration. That's a bug.

For PR KVM guests this is noticable because they no longer do live
patching of themselves, which can be detected by the omission of a
message in dmesg such as:

  KVM: Live patching for a fast VM worked

To fix it make check_kvm_guest() an initcall, to ensure it's always
called at boot. It needs to be core so that it runs before
kvm_guest_init() which is postcore. To be an initcall it needs to return
int, where 0 means success, so update that.

We still call it manually in pSeries_smp_probe(), because that runs
before init calls are run.

Fixes: a21d1becaa3f ("powerpc: Reintroduce is_kvm_guest() as a fast-path check")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210623130514.2543232-1-mpe@ellerman.id.au

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/powerpc/include/asm/kvm_guest.h b/arch/powerpc/include/asm/kvm_guest.h
index 2fca299f7e19..c63105d2c9e7 100644
--- a/arch/powerpc/include/asm/kvm_guest.h
+++ b/arch/powerpc/include/asm/kvm_guest.h
@@ -16,10 +16,10 @@ static inline bool is_kvm_guest(void)
 	return static_branch_unlikely(&kvm_guest);
 }
 
-bool check_kvm_guest(void);
+int check_kvm_guest(void);
 #else
 static inline bool is_kvm_guest(void) { return false; }
-static inline bool check_kvm_guest(void) { return false; }
+static inline int check_kvm_guest(void) { return 0; }
 #endif
 
 #endif /* _ASM_POWERPC_KVM_GUEST_H_ */