[PATCH v5 03/15] KVM: SVM: Disable SEV/SEV-ES if NPT is disabled

Sean Christopherson
2021-04-22T02:11:39Z

Disable SEV and SEV-ES if NPT is disabled. While the APM doesn't clearly
state that NPT is mandatory, it's alluded to by:

The guest page tables, managed by the guest, may mark data memory pages
as either private or shared, thus allowing selected pages to be shared
outside the guest.

And practically speaking, shadow paging can't work since KVM can't read
the guest's page tables.

Fixes: e9df09428996 ("KVM: SVM: Add sev module_param")
Cc: Brijesh Singh <brijesh.singh@amd.com
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/svm/svm.c | 30 +++++++++++++++---------------
1 file changed, 15 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index fed153314aef..0e8489908216 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -970,7 +970,21 @@ static __init int svm_hardware_setup(void)
kvm_enable_efer_bits(EFER_SVME | EFER_LMSLE);
}

- if (IS_ENABLED(CONFIG_KVM_AMD_SEV) && sev) {
+ /*
+ * KVM's MMU doesn't support using 2-level paging for itself, and thus
+ * NPT isn't supported if the host is using 2-level paging since host
+ * CR4 is unchanged on VMRUN.
+ */
+ if (!IS_ENABLED(CONFIG_X86_64) && !IS_ENABLED(CONFIG_X86_PAE))
+ npt_enabled = false;
+
+ if (!boot_cpu_has(X86_FEATURE_NPT))
+ npt_enabled = false;
+
+ kvm_configure_mmu(npt_enabled, get_max_npt_level(), PG_LEVEL_1G);
+ pr_info("kvm: Nested Paging %sabled\n", npt_enabled ? "en" : "dis");
+
+ if (IS_ENABLED(CONFIG_KVM_AMD_SEV) && sev && npt_enabled) {
sev_hardware_setup();
} else {
sev = false;
@@ -985,20 +999,6 @@ static __init int svm_hardware_setup(void)
goto err;
}

- /*
- * KVM's MMU doesn't support using 2-level paging for itself, and thus
- * NPT isn't supported if the host is using 2-level paging since host
- * CR4 is unchanged on VMRUN.
- */
- if (!IS_ENABLED(CONFIG_X86_64) && !IS_ENABLED(CONFIG_X86_PAE))
- npt_enabled = false;
-
- if (!boot_cpu_has(X86_FEATURE_NPT))
- npt_enabled = false;
-
- kvm_configure_mmu(npt_enabled, get_max_npt_level(), PG_LEVEL_1G);
- pr_info("kvm: Nested Paging %sabled\n", npt_enabled ? "en" : "dis");
-
if (nrips) {
if (!boot_cpu_has(X86_FEATURE_NRIPS))
nrips = false;