linux-kernel - [PATCH v1 3/3] KVM: SVM: Add 5-level page table support for SVM

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Date:   Thu,  5 Aug 2021 15:55:04 -0500
From:   Wei Huang <wei.huang2@....com>
To:     kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, pbonzini@...hat.com,
        vkuznets@...hat.com, seanjc@...gle.com, wanpengli@...cent.com,
        jmattson@...gle.com, joro@...tes.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
        wei.huang2@....com
Subject: [PATCH v1 3/3] KVM: SVM: Add 5-level page table support for SVM

Future AMD CPUs will support 5-level page table which is indicated by
X86_CR4_LA57 flag. When the 5-level page table is enabled on host OS,
the nested page table for guest VMs must use 5-level as well. Update
get_npt_level() function to reflect this requirement. In the meanwhile,
remove the code that prevents kvm-amd driver from being loaded when
5-level page table is detected.

Signed-off-by: Wei Huang <wei.huang2@....com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/svm/svm.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 04710e10d04a..f91ff7d2d9f9 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -261,7 +261,9 @@ u32 svm_msrpm_offset(u32 msr)
 static int svm_get_npt_level(struct kvm_vcpu *vcpu)
 {
 #ifdef CONFIG_X86_64
-	return PT64_ROOT_4LEVEL;
+	bool la57 = (cr4_read_shadow() & X86_CR4_LA57) != 0;
+
+	return la57 ? PT64_ROOT_5LEVEL : PT64_ROOT_4LEVEL;
 #else
 	return PT32E_ROOT_LEVEL;
 #endif
@@ -462,11 +464,6 @@ static int has_svm(void)
 		return 0;
 	}
 
-	if (pgtable_l5_enabled()) {
-		pr_info("KVM doesn't yet support 5-level paging on AMD SVM\n");
-		return 0;
-	}
-
 	return 1;
 }
 
-- 
2.31.1