linux-kernel - Re: [RFC 00/12] KVM/X86: Introduce a new guest mapping API

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Date:   Sat, 10 Feb 2018 12:33:41 +0100
From:   KarimAllah Ahmed <karahmed@...zon.com>
To:     Mihai Donțu <mdontu@...defender.com>,
        KarimAllah Ahmed <karahmed@...zon.de>
CC:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>
Subject: Re: [RFC 00/12] KVM/X86: Introduce a new guest mapping API

On 02/05/2018 08:26 PM, Mihai Donțu wrote:
> On Mon, 2018-02-05 at 19:47 +0100, KarimAllah Ahmed wrote:
>> Guest memory can either be directly managed by the kernel (i.e. have a "struct
>> page") or they can simply live outside kernel control (i.e. do not have a
>> "struct page"). KVM mostly support these two modes, except in a few places
>> where the code seems to assume that guest memory must have a "struct page".
> 
> In cases where there is no 'struct page', would it be possible to get
> two VM-s to share memory (in the way Xen's grant tables do)?
> 
> We are working on a page sharing mechanism and would like to know if
> this use case can be accommodated.

If your code is posted somewhere, I can take a look and let you know it
can be accommodated or not.

> 
> Thank you,
> 
>> This patchset introduces a new mapping function to map guest memory into host
>> kernel memory. Ideally I should also get rid of all guest mapping functions
>> that end up converting a guest address to a page, but I decided to get feedback
>> on this first and see if this is an acceptable API.
>>
>> Most of the offending code paths that has been updated are in the nested code
>> base. Mostly because I stumbled upon this code while looking at the nested MSR
>> bitmap handling for the IBRS patches. There are also offending code paths in
>> SVM code, but I will do that once the interface is accepted.
>>
>> KarimAllah Ahmed (12):
>>    KVM: Introduce helper functions to map/unmap guest memory
>>    KVM/VMX: Use the new host mapping API for apic_access_page
>>    KVM/VMX: Use the new host mapping API for virtual_apic_page
>>    KVM/VMX: Use the new host mapping API for pi_desc_page
>>    KVM/VMX: Use the new host mapping API for mapping nested vmptr
>>    KVM/VMX: Use the new host mapping API for handle_vmptrld
>>    KVM/VMX: Use the new host mapping API for mapping L12 MSR bitmap
>>    KVM/VMX: Use the new host mapping API for mapping nested PML
>>    KVM/VMX: Use the new host mapping API for cmpxchg_emulated
>>    KVM/VMX: Use the new host mapping API for synic_clear_sint_msg_pending
>>    KVM/VMX: Use the new host mapping API for synic_deliver_msg
>>    KVM/VMX: Remove kvm_vcpu_gpa_to_page as it is now unused
>>
>>   arch/x86/kvm/hyperv.c    |  24 +++----
>>   arch/x86/kvm/vmx.c       | 159 ++++++++++++++++++++---------------------------
>>   arch/x86/kvm/x86.c       |  12 ++--
>>   include/linux/kvm_host.h |  18 +++++-
>>   virt/kvm/kvm_main.c      |  62 ++++++++++++++++++
>>   5 files changed, 161 insertions(+), 114 deletions(-)
>>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Cc: kvm@...r.kernel.org
>> Cc: linux-kernel@...r.kernel.org
> 
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