linux-kernel - Re: [PATCH 0/3] KVM: VMX: Allow to disable ioport intercept per-VM by userspace

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Message-ID: <c41802dd-8c45-ae00-9b14-b5a04e964f7c@redhat.com>
Date:   Tue, 8 May 2018 18:14:07 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        Tim Shearer <tshearer@...aoptical.com>,
        Liran Alon <liran.alon@...cle.com>
Subject: Re: [PATCH 0/3] KVM: VMX: Allow to disable ioport intercept per-VM by
 userspace

On 08/05/2018 09:55, Wanpeng Li wrote:
> 2018-04-17 13:45 GMT+08:00 Wanpeng Li <kernellwp@...il.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 0x80. 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 patchset introduces per-VM I/O permission bitmaps, the userspace
>> can disable the ioport intercept when they are more concern the
>> performance than the security.
>>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Cc: Tim Shearer <tshearer@...aoptical.com>
>> Cc: Liran Alon <liran.alon@...cle.com>
>>
> 
> Hi Paolo,
> 
> Did you send the patch to glibc or the patchset still can be considered?

I haven't, but I'm still not sure about the usefulness of these patches.

Paolo

> 
> Regards,
> Wanpeng Li
> 
>> Wanpeng Li (3):
>>   KVM: VMX: Introduce per-VM I/O permission bitmaps
>>   KVM: X86: Allow userspace to disable ioport intercept
>>   KVM: VMX: Allow I/O port 0x80 bypass when userspace prefer
>>
>>  Documentation/virtual/kvm/api.txt | 11 +++++++++++
>>  arch/x86/include/asm/kvm_host.h   |  2 ++
>>  arch/x86/kvm/vmx.c                | 41 ++++++++++++++++++++++++++++++++++++---
>>  arch/x86/kvm/x86.c                |  5 +++++
>>  include/uapi/linux/kvm.h          |  1 +
>>  5 files changed, 57 insertions(+), 3 deletions(-)
>>
>> --
>> 2.7.4
>>