linux-kernel - Re: [PATCH v6 00/14] KVM/X86: Introduce a new guest mapping interface

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Date:   Mon, 18 Mar 2019 13:10:24 +0000
From:   "Raslan, KarimAllah" <karahmed@...zon.de>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH v6 00/14] KVM/X86: Introduce a new guest mapping interface

I guess this patch series missed the 5.1 merge window? :)

On Thu, 2019-01-31 at 21:24 +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".
> 
> 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. Patch 2 is additionally fixing an
> incorrect page release and marking the page as dirty (i.e. as a side-effect of
> using the helper function to write).
> 
> 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.
> 
> So the simple way to use memory outside kernel control is:
> 
> 1- Pass 'mem=' in the kernel command-line to limit the amount of memory managed 
>    by the kernel.
> 2- Map this physical memory you want to give to the guest with:
>    mmap("/dev/mem", physical_address_offset, ..)
> 3- Use the user-space virtual address as the "userspace_addr" field in
>    KVM_SET_USER_MEMORY_REGION ioctl.
> 
> v5 -> v6:
> - Added one extra patch to ensure that support for this mem= case is complete
>   for x86.
> - Added a helper function to check if the mapping is mapped or not.
> - Added more comments on the struct.
> - Setting ->page to NULL on unmap and to a poison ptr if unused during map
> - Checking for map ptr before using it.
> - Change kvm_vcpu_unmap to also mark page dirty for LM. That requires
>   passing the vCPU pointer again to this function.
> 
> v4 -> v5:
> - Introduce a new parameter 'dirty' into kvm_vcpu_unmap
> - A horrible rebase due to nested.c :)
> - Dropped a couple of hyperv patches as the code was fixed already as a
>   side-effect of another patch.
> - Added a new trivial cleanup patch.
> 
> v3 -> v4:
> - Rebase
> - Add a new patch to also fix the newly introduced enlightned VMCS.
> 
> 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: Update the PML table without mapping and unmapping the page
>   KVM: Introduce a new guest mapping API
>   X86/nVMX: handle_vmptrld: Use kvm_vcpu_map when copying VMCS12 from
>     guest memory
>   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/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 enlightened VMCS
>   KVM/nVMX: Use page_address_valid in a few more locations
>   kvm, x86: Properly check whether a pfn is an MMIO or not
> 
>  arch/x86/include/asm/e820/api.h |   1 +
>  arch/x86/kernel/e820.c          |  18 ++++-
>  arch/x86/kvm/mmu.c              |   5 +-
>  arch/x86/kvm/paging_tmpl.h      |  38 +++++++---
>  arch/x86/kvm/svm.c              |  97 ++++++++++++------------
>  arch/x86/kvm/vmx/nested.c       | 160 +++++++++++++++-------------------------
>  arch/x86/kvm/vmx/vmx.c          |  19 ++---
>  arch/x86/kvm/vmx/vmx.h          |   9 ++-
>  arch/x86/kvm/x86.c              |  14 ++--
>  include/linux/kvm_host.h        |  28 +++++++
>  virt/kvm/kvm_main.c             |  64 ++++++++++++++++
>  11 files changed, 267 insertions(+), 186 deletions(-)
> 



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