linux-kernel - [PATCH 5.10 211/289] kvm: exit halt polling on need

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Message-Id: <20210517140312.226734512@linuxfoundation.org>
Date:   Mon, 17 May 2021 16:02:16 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ben Segall <bsegall@...gle.com>,
        Venkatesh Srinivas <venkateshs@...omium.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>
Subject: [PATCH 5.10 211/289] kvm: exit halt polling on need_resched() as well

From: Benjamin Segall <bsegall@...gle.com>

commit 262de4102c7bb8e59f26a967a8ffe8cce85cc537 upstream.

single_task_running() is usually more general than need_resched()
but CFS_BANDWIDTH throttling will use resched_task() when there
is just one task to get the task to block. This was causing
long-need_resched warnings and was likely allowing VMs to
overrun their quota when halt polling.

Signed-off-by: Ben Segall <bsegall@...gle.com>
Signed-off-by: Venkatesh Srinivas <venkateshs@...omium.org>
Message-Id: <20210429162233.116849-1-venkateshs@...omium.org>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Cc: stable@...r.kernel.org
Reviewed-by: Jim Mattson <jmattson@...gle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 virt/kvm/kvm_main.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2797,7 +2797,8 @@ void kvm_vcpu_block(struct kvm_vcpu *vcp
 				goto out;
 			}
 			poll_end = cur = ktime_get();
-		} while (single_task_running() && ktime_before(cur, stop));
+		} while (single_task_running() && !need_resched() &&
+			 ktime_before(cur, stop));
 	}
 
 	prepare_to_rcuwait(&vcpu->wait);