linux-kernel - [PATCH v3] KVM: arm64: Ignore kvm-arm.mode if !is_hyp_mode

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Message-ID: <20220911214059.2767620-1-quic_eberman@quicinc.com>
Date:   Sun, 11 Sep 2022 14:40:59 -0700
From:   Elliot Berman <quic_eberman@...cinc.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        "Alexandru Elisei" <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>
CC:     Elliot Berman <quic_eberman@...cinc.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <kvmarm@...ts.cs.columbia.edu>
Subject: [PATCH v3] KVM: arm64: Ignore kvm-arm.mode if !is_hyp_mode_available()

Ignore kvm-arm.mode if !is_hyp_mode_available(). Specifically, we want
to avoid switching kvm_mode to KVM_MODE_PROTECTED if hypervisor mode is
not available. This prevents "Protected KVM" cpu capability being
reported when Linux is booting in EL1 and would not have KVM enabled.
Reasonably though, we should warn if the command line is requesting a
KVM mode at all if KVM isn't actually available. Don't emit warning for
"kvm-arm.mode=none" since this would disable KVM anyway.

Signed-off-by: Elliot Berman <quic_eberman@...cinc.com>
---
 arch/arm64/kvm/arm.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 8fe73ee5fa84..8e5d1c8502f5 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -2271,6 +2271,16 @@ static int __init early_kvm_mode_cfg(char *arg)
 	if (!arg)
 		return -EINVAL;
 
+	if (strcmp(arg, "none") == 0) {
+		kvm_mode = KVM_MODE_NONE;
+		return 0;
+	}
+
+	if (!is_hyp_mode_available()) {
+		pr_warn_once("KVM is not available. Ignoring kvm-arm.mode\n")
+		return 0;
+	}
+
 	if (strcmp(arg, "protected") == 0) {
 		if (!is_kernel_in_hyp_mode())
 			kvm_mode = KVM_MODE_PROTECTED;
@@ -2285,11 +2295,6 @@ static int __init early_kvm_mode_cfg(char *arg)
 		return 0;
 	}
 
-	if (strcmp(arg, "none") == 0) {
-		kvm_mode = KVM_MODE_NONE;
-		return 0;
-	}
-
 	return -EINVAL;
 }
 early_param("kvm-arm.mode", early_kvm_mode_cfg);

base-commit: 0982c8d859f8f7022b9fd44d421c7ec721bb41f9
-- 
2.25.1