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

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Date:   Tue, 12 Dec 2017 16:39:30 +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 2017/12/12 02:08, Jim Mattson wrote:
> Removing these two lines from the initialization of
> field_to_offset_table[] means that vmcs_field_to_offset() will return
> -ENOENT for IO_BITMAP_A or IO_BITMAP_B. Hence, handle_vmread and
> handle_vmwrite will incorrectly report these fields as unsupported
> VMCS components if an L1 hypervisor tries to access them.

I will fix in v2.

Quan
Alibaba Cloud



> On Sun, Dec 10, 2017 at 9:37 PM, Quan Xu <quan.xu0@...il.com> wrote:
>>
>> 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?
>>
>> Alibaba Cloud
>> Quan
>>
>>
>>