linux-kernel - Re: [PATCH v13 08/35] KVM: Introduce KVM_SET_USER_MEMORY

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Message-ID: <ZUEJg_rBf35NyCG3@google.com>
Date:   Tue, 31 Oct 2023 07:04:51 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Huacai Chen <chenhuacai@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Anup Patel <anup@...infault.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>, kvm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Xu Yilun <yilun.xu@...el.com>,
        Chao Peng <chao.p.peng@...ux.intel.com>,
        Fuad Tabba <tabba@...gle.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Anish Moorthy <amoorthy@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        Isaku Yamahata <isaku.yamahata@...el.com>,
        "Mickaël Salaün" <mic@...ikod.net>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Ackerley Tng <ackerleytng@...gle.com>,
        Maciej Szmigiero <mail@...iej.szmigiero.name>,
        David Hildenbrand <david@...hat.com>,
        Quentin Perret <qperret@...gle.com>,
        Michael Roth <michael.roth@....com>,
        Wang <wei.w.wang@...el.com>,
        Liam Merwick <liam.merwick@...cle.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v13 08/35] KVM: Introduce KVM_SET_USER_MEMORY_REGION2

On Tue, Oct 31, 2023, Xiaoyao Li wrote:
> On 10/28/2023 2:21 AM, Sean Christopherson wrote:
> > Introduce a "version 2" of KVM_SET_USER_MEMORY_REGION so that additional
> > information can be supplied without setting userspace up to fail.  The
> > padding in the new kvm_userspace_memory_region2 structure will be used to
> > pass a file descriptor in addition to the userspace_addr, i.e. allow
> > userspace to point at a file descriptor and map memory into a guest that
> > is NOT mapped into host userspace.
> > 
> > Alternatively, KVM could simply add "struct kvm_userspace_memory_region2"
> > without a new ioctl(), but as Paolo pointed out, adding a new ioctl()
> > makes detection of bad flags a bit more robust, e.g. if the new fd field
> > is guarded only by a flag and not a new ioctl(), then a userspace bug
> > (setting a "bad" flag) would generate out-of-bounds access instead of an
> > -EINVAL error.
> > 
> > Cc: Jarkko Sakkinen <jarkko@...nel.org>
> > Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
> > Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>
> > Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> > ---
> >   Documentation/virt/kvm/api.rst | 21 +++++++++++++++++++
> >   arch/x86/kvm/x86.c             |  2 +-
> >   include/linux/kvm_host.h       |  4 ++--
> >   include/uapi/linux/kvm.h       | 13 ++++++++++++
> >   virt/kvm/kvm_main.c            | 38 +++++++++++++++++++++++++++-------
> >   5 files changed, 67 insertions(+), 11 deletions(-)
> > 
> > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> > index 21a7578142a1..ace984acc125 100644
> > --- a/Documentation/virt/kvm/api.rst
> > +++ b/Documentation/virt/kvm/api.rst
> > @@ -6070,6 +6070,27 @@ writes to the CNTVCT_EL0 and CNTPCT_EL0 registers using the SET_ONE_REG
> >   interface. No error will be returned, but the resulting offset will not be
> >   applied.
> > +4.139 KVM_SET_USER_MEMORY_REGION2
> > +---------------------------------
> > +
> > +:Capability: KVM_CAP_USER_MEMORY2
> > +:Architectures: all
> > +:Type: vm ioctl
> > +:Parameters: struct kvm_userspace_memory_region2 (in)
> > +:Returns: 0 on success, -1 on error
> > +
> > +::
> > +
> > +  struct kvm_userspace_memory_region2 {
> > +	__u32 slot;
> > +	__u32 flags;
> > +	__u64 guest_phys_addr;
> > +	__u64 memory_size; /* bytes */
> > +	__u64 userspace_addr; /* start of the userspace allocated memory */
> 
> missing
> 
> 	__u64 pad[16];

I can't even copy+paste correctly :-(