linux-kernel - Re: [PATCH v4 00/14] KVM/X86: Introduce a new guest mapping interface

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Message-ID: <249a6d5e-5a07-8626-da86-e37f6eb31f90@redhat.com>
Date:   Fri, 21 Dec 2018 16:22:34 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     KarimAllah Ahmed <karahmed@...zon.de>, rkrcmar@...hat.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        jmattson@...gle.com
Subject: Re: [PATCH v4 00/14] KVM/X86: Introduce a new guest mapping interface

On 03/12/18 10:30, 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".
> 
> This patchset introduces a new mapping interface to map guest memory into host
> kernel memory which also supports PFN-based memory (i.e. memory without 'struct
> page'). It also converts all offending code to this interface or simply
> read/write directly from guest memory.
> 
> As far as I can see all offending code is now fixed except the APIC-access page
> which I will handle in a seperate series along with dropping
> kvm_vcpu_gfn_to_page and kvm_vcpu_gpa_to_page from the internal KVM API.
> 
> The current implementation of the new API uses memremap to map memory that does
> not have a "struct page". This proves to be very slow for high frequency
> mappings. Since this does not affect the normal use-case where a "struct page"
> is available, the performance of this API will be handled by a seperate patch
> series.
> 
> v3 -> v4:
> - Rebase
> - Add a new patch to also fix the newly introduced enhanced VMCS.

This will need a few more changes (especially given the review remarks
for patch 2), so please also add the separate dirty/clean unmap APIs in
the next revision.

In order to rebase against the vmx.c split, my suggestion is that you
first rebase to the last commit before nested.c was separated, then on
the immediately following one, and then on the top of the tree.  Most of
the time, "patch -p1 arch/x86/kvm/vmx/nested.c <
.git/rebase-apply/patch" will do the right thing.

Paolo

> v2 -> v3:
> - Rebase
> - Add a new patch to also fix the newly introduced shadow VMCS.
> 
> Filippo Sironi (1):
>   X86/KVM: Handle PFNs outside of kernel reach when touching GPTEs
> 
> KarimAllah Ahmed (13):
>   X86/nVMX: handle_vmon: Read 4 bytes from guest memory
>   X86/nVMX: handle_vmptrld: Copy the VMCS12 directly from guest memory
>   X86/nVMX: Update the PML table without mapping and unmapping the page
>   KVM: Introduce a new guest mapping API
>   KVM/nVMX: Use kvm_vcpu_map when mapping the L1 MSR bitmap
>   KVM/nVMX: Use kvm_vcpu_map when mapping the virtual APIC page
>   KVM/nVMX: Use kvm_vcpu_map when mapping the posted interrupt
>     descriptor table
>   KVM/X86: Use kvm_vcpu_map in emulator_cmpxchg_emulated
>   KVM/X86: hyperv: Use kvm_vcpu_map in synic_clear_sint_msg_pending
>   KVM/X86: hyperv: Use kvm_vcpu_map in synic_deliver_msg
>   KVM/nSVM: Use the new mapping API for mapping guest memory
>   KVM/nVMX: Use kvm_vcpu_map for accessing the shadow VMCS
>   KVM/nVMX: Use kvm_vcpu_map for accessing the enhanced VMCS
> 
>  arch/x86/kvm/hyperv.c      |  28 +++----
>  arch/x86/kvm/paging_tmpl.h |  38 ++++++---
>  arch/x86/kvm/svm.c         |  97 +++++++++++------------
>  arch/x86/kvm/vmx.c         | 189 +++++++++++++++++----------------------------
>  arch/x86/kvm/x86.c         |  13 ++--
>  include/linux/kvm_host.h   |   9 +++
>  virt/kvm/kvm_main.c        |  50 ++++++++++++
>  7 files changed, 228 insertions(+), 196 deletions(-)
>