powerpc: Fix is_kvm_guest() / kvm_para_available()

Commit 2f59ab143f69 ("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: 2f59ab143f69 ("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

diff --git a/arch/powerpc/include/asm/kvm_guest.h b/arch/powerpc/include/asm/kvm_guest.h
index 2fca299f7e1929e6f1f1f3dac6b86c1fb1c85c9e..c63105d2c9e7c3cf8fec91f130088a1a6418ea92 100644 (file)
--- 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_ */

diff --git a/arch/powerpc/kernel/firmware.c b/arch/powerpc/kernel/firmware.c
index c9e2819b095abb23a52169f5e9ff0f17b6aab911..c7022c41cc314945c908ed6abc4aa95e03d63261 100644 (file)
--- a/arch/powerpc/kernel/firmware.c
+++ b/arch/powerpc/kernel/firmware.c
@@ -23,18 +23,20 @@ EXPORT_SYMBOL_GPL(powerpc_firmware_features);
 
 #if defined(CONFIG_PPC_PSERIES) || defined(CONFIG_KVM_GUEST)
 DEFINE_STATIC_KEY_FALSE(kvm_guest);
-bool check_kvm_guest(void)
+int __init check_kvm_guest(void)
 {
        struct device_node *hyper_node;
 
        hyper_node = of_find_node_by_path("/hypervisor");
        if (!hyper_node)
-               return false;
+               return 0;
 
        if (!of_device_is_compatible(hyper_node, "linux,kvm"))
-               return false;
+               return 0;
 
        static_branch_enable(&kvm_guest);
-       return true;
+
+       return 0;
 }
+core_initcall(check_kvm_guest); // before kvm_guest_init()
 #endif

diff --git a/arch/powerpc/platforms/pseries/smp.c b/arch/powerpc/platforms/pseries/smp.c
index c70b4be9f0a5496a8f16a633d09aee3193e2076a..096629f545769fe97729ae5cef8e4a1590859241 100644 (file)
--- a/arch/powerpc/platforms/pseries/smp.c
+++ b/arch/powerpc/platforms/pseries/smp.c
@@ -211,7 +211,9 @@ static __init void pSeries_smp_probe(void)
        if (!cpu_has_feature(CPU_FTR_SMT))
                return;
 
-       if (check_kvm_guest()) {
+       check_kvm_guest();
+
+       if (is_kvm_guest()) {
                /*
                 * KVM emulates doorbells by disabling FSCR[MSGP] so msgsndp
                 * faults to the hypervisor which then reads the instruction