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

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Message-ID: <20190318142232.GC16697@char.us.oracle.com>
Date:   Mon, 18 Mar 2019 10:22:32 -0400
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     "Raslan, KarimAllah" <karahmed@...zon.de>
Cc:     "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

On Mon, Mar 18, 2019 at 01:10:24PM +0000, Raslan, KarimAllah wrote:
> I guess this patch series missed the 5.1 merge window? :)

Were there any outstanding fixes that had to be addressed?

> 
> 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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