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>
---
 arch/x86/kernel/cpu/mshyperv.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 26b9fcabd7d95..c8d3ca2b0e0ee 100644
--- 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);
 		}
 	}
 
-- 
2.25.1

On Tue, Aug 22, 2023 at 08:20:08PM -0700, Dexuan Cui wrote:
> 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>

Applied. Thanks.