linux-kernel - Re: [PATCH] KVM: VMX: drop I/O permission bitmaps

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Date:   Mon, 11 Dec 2017 13:37:55 +0800
From:   Quan Xu <quan.xu0@...il.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH] KVM: VMX: drop I/O permission bitmaps



On 2017/12/09 01:31, Jim Mattson wrote:
> On Fri, Dec 8, 2017 at 2:22 AM, Quan Xu <quan.xu0@...il.com> wrote:
>> From: Quan Xu <quan.xu0@...il.com>
>>
>> Since KVM removes the only I/O port 0x80 bypass on Intel hosts,
>> clear CPU_BASED_USE_IO_BITMAPS and set CPU_BASED_UNCOND_IO_EXITING
>> bit. Then these I/O permission bitmaps are not used at all, so
>> drop I/O permission bitmaps.
>>
>> Signed-off-by: Jim Mattson <jmattson@...gle.com>
>> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
>> Signed-off-by: Quan Xu <quan.xu0@...il.com>
>> ---
>>   arch/x86/kvm/vmx.c |   17 +----------------
>>   1 files changed, 1 insertions(+), 16 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 2fd9a8c..3e4f760 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -771,8 +771,6 @@ enum segment_cache_field {
>>          FIELD(HOST_FS_SELECTOR, host_fs_selector),
>>          FIELD(HOST_GS_SELECTOR, host_gs_selector),
>>          FIELD(HOST_TR_SELECTOR, host_tr_selector),
>> -       FIELD64(IO_BITMAP_A, io_bitmap_a),
>> -       FIELD64(IO_BITMAP_B, io_bitmap_b),
> These two lines should stay.
Jim, could you explain why these two lines should stay?


IIUC, the main concern is from  nested virtualization, which still uses 
io_bitmap_a/io_bitmap_b..
if so, we really need to further clean up these code, as

CPU_BASED_USE_IO_BITMAPS is clear, and CPU_BASED_UNCOND_IO_EXITING is set for both L0/L2. after new patches which I mentioned
in this thread.

right?

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