linux-kernel - Re: [RFC 07/16] KVM: mm: Introduce VM_KVM

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Date:   Wed, 27 May 2020 01:01:55 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        David Rientjes <rientjes@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Will Drewry <wad@...omium.org>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "Kleen, Andi" <andi.kleen@...el.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [RFC 07/16] KVM: mm: Introduce VM_KVM_PROTECTED

On Tue, May 26, 2020 at 09:15:52AM +0300, Mike Rapoport wrote:
> On Fri, May 22, 2020 at 03:52:05PM +0300, Kirill A. Shutemov wrote:
> > The new VMA flag that indicate a VMA that is not accessible to userspace
> > but usable by kernel with GUP if FOLL_KVM is specified.
> > 
> > The FOLL_KVM is only used in the KVM code. The code has to know how to
> > deal with such pages.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > ---
> >  include/linux/mm.h  |  8 ++++++++
> >  mm/gup.c            | 20 ++++++++++++++++----
> >  mm/huge_memory.c    | 20 ++++++++++++++++----
> >  mm/memory.c         |  3 +++
> >  mm/mmap.c           |  3 +++
> >  virt/kvm/async_pf.c |  4 ++--
> >  virt/kvm/kvm_main.c |  9 +++++----
> >  7 files changed, 53 insertions(+), 14 deletions(-)
> > 
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index e1882eec1752..4f7195365cc0 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -329,6 +329,8 @@ extern unsigned int kobjsize(const void *objp);
> >  # define VM_MAPPED_COPY	VM_ARCH_1	/* T if mapped copy of data (nommu mmap) */
> >  #endif
> >  
> > +#define VM_KVM_PROTECTED 0
> 
> With all the ideas about removing pages from the direct mapi floating
> around I wouldn't limit this to KVM.
> 
> VM_NOT_IN_DIRECT_MAP would describe such areas better, but I realise
> it's very far from perfect and nothing better does not comes to mind :)

I don't like VM_NOT_IN_DIRECT_MAP.

It's not only about direct mapping, but about userspace mapping as well.
For the same reason other naming proposals don't fit as well.

> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index f609e9ec4a25..d56c3f6efc99 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -112,6 +112,9 @@ pgprot_t vm_get_page_prot(unsigned long vm_flags)
> >  				(VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]) |
> >  			pgprot_val(arch_vm_get_page_prot(vm_flags)));
> >  
> > +	if (vm_flags & VM_KVM_PROTECTED)
> > +		ret = PAGE_NONE;
> 
> Nit: vma_is_kvm_protected()?

Which VMA? :P

-- 
 Kirill A. Shutemov