x86/hyperv: Fix undefined reference to isolation_type_en_snp without CONFIG_HYPERV

When CONFIG_HYPERV is not set, arch/x86/hyperv/ivm.c is not built (see
arch/x86/Kbuild), so 'isolation_type_en_snp' in the ivm.c is not defined,
and this failure happens:

ld: arch/x86/kernel/cpu/mshyperv.o: in function `ms_hyperv_init_platform':
arch/x86/kernel/cpu/mshyperv.c:417: undefined reference to `isolation_type_en_snp'

Fix the failure by testing hv_get_isolation_type() and
ms_hyperv.paravisor_present for a fully enlightened SNP VM: when
CONFIG_HYPERV is not set, hv_get_isolation_type() is defined as a
static inline function that always returns HV_ISOLATION_TYPE_NONE
(see include/asm-generic/mshyperv.h), so the compiler won't generate any
code for the ms_hyperv.paravisor_present and static_branch_enable().

Reported-by: Tom Lendacky <thomas.lendacky@amd.com>
Closes: https://lore.kernel.org/lkml/b4979997-23b9-0c43-574e-e4a3506500ff@amd.com/
Fixes: d6e2d6524437 ("x86/hyperv: Add sev-snp enlightened guest static key")
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Link: https://lore.kernel.org/r/20230823032008.18186-1-decui@microsoft.com

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 26b9fcabd7d95b1bea38d5bf95c109d477d27fdb..c8d3ca2b0e0eefbb30e666422b11fb8324ea814c 100644 (file)
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -413,10 +413,11 @@ static void __init ms_hyperv_init_platform(void)
                        ms_hyperv.isolation_config_a, ms_hyperv.isolation_config_b);
 
 
-               if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP)) {
-                       static_branch_enable(&isolation_type_en_snp);
-               } else if (hv_get_isolation_type() == HV_ISOLATION_TYPE_SNP) {
-                       static_branch_enable(&isolation_type_snp);
+               if (hv_get_isolation_type() == HV_ISOLATION_TYPE_SNP) {
+                       if (ms_hyperv.paravisor_present)
+                               static_branch_enable(&isolation_type_snp);
+                       else
+                               static_branch_enable(&isolation_type_en_snp);
                }
        }