[PATCH] KVM: arm64: Ratelimit error log during guest debug exception

Subsystems: arm64 port (aarch64 architecture), kernel virtual machine for arm64 (kvm/arm64), the rest

STALE1819d

2 messages, 2 authors, 2021-08-20 · open the first message on its own page

[PATCH] KVM: arm64: Ratelimit error log during guest debug exception

From: Raghavendra Rao Ananta <hidden>
Date: 2021-08-19 22:34:18

Potentially, the guests could trigger a debug exception that's
outside the exception class range. This could lead to an
excessive syslog flooding. Hence, ratelimit the error message.

Signed-off-by: Raghavendra Rao Ananta <redacted>
---
 arch/arm64/kvm/handle_exit.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index 04ebab299aa4..c7cec7ffe93c 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -134,7 +134,7 @@ static int kvm_handle_guest_debug(struct kvm_vcpu *vcpu)
 	case ESR_ELx_EC_BRK64:
 		break;
 	default:
-		kvm_err("%s: un-handled case esr: %#08x\n",
+		kvm_pr_unimpl("%s: un-handled case esr: %#08x\n",
 			__func__, (unsigned int) esr);
 		ret = -1;
 		break;
-- 
2.33.0.rc2.250.ged5fa647cd-goog


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Re: [PATCH] KVM: arm64: Ratelimit error log during guest debug exception

From: Marc Zyngier <maz@kernel.org>
Date: 2021-08-20 09:29:58

On Thu, 19 Aug 2021 23:34:06 +0100,
Raghavendra Rao Ananta [off-list ref] wrote:
Potentially, the guests could trigger a debug exception that's
outside the exception class range.
How? All the exception classes that lead to this functions are already
handled in the switch/case statement.
quoted hunk
This could lead to an excessive syslog flooding. Hence, ratelimit
the error message.

Signed-off-by: Raghavendra Rao Ananta <redacted>
---
 arch/arm64/kvm/handle_exit.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index 04ebab299aa4..c7cec7ffe93c 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -134,7 +134,7 @@ static int kvm_handle_guest_debug(struct kvm_vcpu *vcpu)
 	case ESR_ELx_EC_BRK64:
 		break;
 	default:
-		kvm_err("%s: un-handled case esr: %#08x\n",
+		kvm_pr_unimpl("%s: un-handled case esr: %#08x\n",
 			__func__, (unsigned int) esr);
 		ret = -1;
 		break;
My take on this is that this code isn't reachable, and that it could
be better rewritten as:
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index 6f48336b1d86..ae7ec086827b 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -119,28 +119,14 @@ static int kvm_handle_guest_debug(struct kvm_vcpu *vcpu)
 {
 	struct kvm_run *run = vcpu->run;
 	u32 esr = kvm_vcpu_get_esr(vcpu);
-	int ret = 0;
 
 	run->exit_reason = KVM_EXIT_DEBUG;
 	run->debug.arch.hsr = esr;
 
-	switch (ESR_ELx_EC(esr)) {
-	case ESR_ELx_EC_WATCHPT_LOW:
+	if (ESR_ELx_EC(esr) ==  ESR_ELx_EC_WATCHPT_LOW)
 		run->debug.arch.far = vcpu->arch.fault.far_el2;
-		fallthrough;
-	case ESR_ELx_EC_SOFTSTP_LOW:
-	case ESR_ELx_EC_BREAKPT_LOW:
-	case ESR_ELx_EC_BKPT32:
-	case ESR_ELx_EC_BRK64:
-		break;
-	default:
-		kvm_err("%s: un-handled case esr: %#08x\n",
-			__func__, (unsigned int) esr);
-		ret = -1;
-		break;
-	}
 
-	return ret;
+	return 0;
 }
 
 static int kvm_handle_unknown_ec(struct kvm_vcpu *vcpu)
Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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