2020-07-31 20:53:53

by Sean Christopherson

Subject: [RFC PATCH] KVM: SVM: Disallow SEV if NPT is disabled

Forcefully turn off SEV if NPT is disabled, e.g. via module param. SEV
requires NPT as the C-bit only exists if NPT is active.

Fixes: e9df09428996f ("KVM: SVM: Add sev module_param")
Cc: [email protected]
Cc: Tom Lendacky <[email protected]>
Cc: Brijesh Singh <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---

RFC as it's entirely possible that I am completely misunderstanding how
SEV works. Compile tested only.

arch/x86/kvm/svm/svm.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 783330d0e7b88..e30629593458b 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -860,8 +860,14 @@ static __init int svm_hardware_setup(void)
kvm_enable_efer_bits(EFER_SVME | EFER_LMSLE);
}

+ if (!boot_cpu_has(X86_FEATURE_NPT))
+ npt_enabled = false;
+
+ if (npt_enabled && !npt)
+ npt_enabled = false;
+
if (sev) {
- if (boot_cpu_has(X86_FEATURE_SEV) &&
+ if (boot_cpu_has(X86_FEATURE_SEV) && npt_enabled &&
IS_ENABLED(CONFIG_KVM_AMD_SEV)) {
r = sev_hardware_setup();
if (r)
@@ -879,12 +885,6 @@ static __init int svm_hardware_setup(void)
goto err;
}

- if (!boot_cpu_has(X86_FEATURE_NPT))
- npt_enabled = false;
-
- if (npt_enabled && !npt)
- npt_enabled = false;
-
kvm_configure_mmu(npt_enabled, PG_LEVEL_1G);
pr_info("kvm: Nested Paging %sabled\n", npt_enabled ? "en" : "dis");

--
2.28.0

2020-08-04 15:17:50

by Brijesh Singh

Subject: Re: [RFC PATCH] KVM: SVM: Disallow SEV if NPT is disabled

On 7/31/20 3:51 PM, Sean Christopherson wrote:
> Forcefully turn off SEV if NPT is disabled, e.g. via module param. SEV
> requires NPT as the C-bit only exists if NPT is active.
>
> Fixes: e9df09428996f ("KVM: SVM: Add sev module_param")
> Cc: [email protected]
> Cc: Tom Lendacky <[email protected]>
> Cc: Brijesh Singh <[email protected]>
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
>
> RFC as it's entirely possible that I am completely misunderstanding how
> SEV works. Compile tested only.


Reviewed-By: Brijesh Singh <[email protected]>


>
> arch/x86/kvm/svm/svm.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 783330d0e7b88..e30629593458b 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -860,8 +860,14 @@ static __init int svm_hardware_setup(void)
> kvm_enable_efer_bits(EFER_SVME | EFER_LMSLE);
> }
>
> + if (!boot_cpu_has(X86_FEATURE_NPT))
> + npt_enabled = false;
> +
> + if (npt_enabled && !npt)
> + npt_enabled = false;
> +
> if (sev) {
> - if (boot_cpu_has(X86_FEATURE_SEV) &&
> + if (boot_cpu_has(X86_FEATURE_SEV) && npt_enabled &&
> IS_ENABLED(CONFIG_KVM_AMD_SEV)) {
> r = sev_hardware_setup();
> if (r)
> @@ -879,12 +885,6 @@ static __init int svm_hardware_setup(void)
> goto err;
> }
>
> - if (!boot_cpu_has(X86_FEATURE_NPT))
> - npt_enabled = false;
> -
> - if (npt_enabled && !npt)
> - npt_enabled = false;
> -
> kvm_configure_mmu(npt_enabled, PG_LEVEL_1G);
> pr_info("kvm: Nested Paging %sabled\n", npt_enabled ? "en" : "dis");
>