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

[KarimAllah Ahmed]

On 02/05/2018 08:26 PM, Mihai DonÈu 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@xxxxxxxxxx>
> > Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
> > Cc: kvm@xxxxxxxxxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
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