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From: Wanpeng Li <kernellwp@gmail.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"Tim Shearer" <tshearer@advaoptical.com>,
	"Liran Alon" <liran.alon@oracle.com>
Subject: [PATCH 3/3] KVM: VMX: Allow I/O port 0x80 bypass when userspace prefer
Date: Mon, 16 Apr 2018 22:46:02 -0700	[thread overview]
Message-ID: <1523943962-25415-4-git-send-email-wanpengli@tencent.com> (raw)
In-Reply-To: <1523943962-25415-1-git-send-email-wanpengli@tencent.com>

From: Wanpeng Li <wanpengli@tencent.com>

Tim Shearer reported that "There is a guest which is running a packet 
forwarding app based on the DPDK (dpdk.org). The packet receive routine 
writes to 0xc070 using glibc's "outw_p" function which does an additional 
write to I/O port 80. It does this write for every packet that's received, 
causing a flood of KVM userspace context switches". He uses mpstat to 
observe a CPU performing L2 packet forwarding on a pinned guest vCPU, 
the guest time is 95 percent when allowing I/O port 0x80 bypass, however, 
it is 65.78 percent when I/O port 0x80 bypss is disabled.  

This patch allows I/O port 0x80 bypass when userspace prefer.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Tim Shearer <tshearer@advaoptical.com>
Cc: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
 arch/x86/kvm/vmx.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index ebf1140..d3e5fef 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -10118,6 +10118,13 @@ static int vmx_vm_init(struct kvm *kvm)
 			goto out;
 		memset(kvm_vmx->vmx_io_bitmap[i], 0xff, PAGE_SIZE);
 	}
+	if (kvm->arch.ioport_disable_intercept)	{
+		/*
+		 * Allow direct access to the PC debug port (it is often used for I/O
+		 * delays, but the vmexits simply slow things down).
+		 */
+		clear_bit(0x80, kvm_vmx->vmx_io_bitmap[VMX_IO_BITMAP_A]);
+	}
 	return 0;
 
 out:
-- 
2.7.4

  parent reply	other threads:[~2018-04-17  5:47 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-17  5:45 [PATCH 0/3] KVM: VMX: Allow to disable ioport intercept per-VM by userspace Wanpeng Li
2018-04-17  5:46 ` [PATCH 1/3] KVM: VMX: Introduce per-VM I/O permission bitmaps Wanpeng Li
2018-05-11 15:39   ` Konrad Rzeszutek Wilk
2018-05-15 21:55     ` Jim Mattson
2018-04-17  5:46 ` [PATCH 2/3] KVM: X86: Allow userspace to disable ioport intercept Wanpeng Li
2018-05-11 15:42   ` Konrad Rzeszutek Wilk
2018-05-11 15:43     ` Konrad Rzeszutek Wilk
2018-05-15 21:56       ` Jim Mattson
2018-05-16  1:13         ` Wanpeng Li
2018-04-17  5:46 ` Wanpeng Li [this message]
2018-05-11 15:44   ` [PATCH 3/3] KVM: VMX: Allow I/O port 0x80 bypass when userspace prefer Konrad Rzeszutek Wilk
2018-05-15 21:57     ` Jim Mattson
2018-05-08  7:55 ` [PATCH 0/3] KVM: VMX: Allow to disable ioport intercept per-VM by userspace Wanpeng Li
2018-05-08 16:14   ` Paolo Bonzini
2018-05-11 15:40 ` Konrad Rzeszutek Wilk
2018-05-12  1:03   ` Wanpeng Li
2018-05-14 13:48     ` Tim Shearer

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