Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 7 Dec 2022 23:11:53 +0800
From:   Chao Peng <chao.p.peng@linux.intel.com>
To:     Fuad Tabba <tabba@google.com>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
        linux-arch@vger.kernel.org, linux-api@vger.kernel.org,
        linux-doc@vger.kernel.org, qemu-devel@nongnu.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Arnd Bergmann <arnd@arndb.de>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        Miaohe Lin <linmiaohe@huawei.com>, x86@kernel.org,
        "H . Peter Anvin" <hpa@zytor.com>, Hugh Dickins <hughd@google.com>,
        Jeff Layton <jlayton@kernel.org>,
        "J . Bruce Fields" <bfields@fieldses.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Shuah Khan <shuah@kernel.org>, Mike Rapoport <rppt@kernel.org>,
        Steven Price <steven.price@arm.com>,
        "Maciej S . Szmigiero" <mail@maciej.szmigiero.name>,
        Vlastimil Babka <vbabka@suse.cz>,
        Vishal Annapurve <vannapurve@google.com>,
        Yu Zhang <yu.c.zhang@linux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com,
        ak@linux.intel.com, david@redhat.com, aarcange@redhat.com,
        ddutile@redhat.com, dhildenb@redhat.com,
        Quentin Perret <qperret@google.com>,
        Michael Roth <michael.roth@amd.com>, mhocko@suse.com,
        wei.w.wang@intel.com
Subject: Re: [PATCH v10 4/9] KVM: Add KVM_EXIT_MEMORY_FAULT exit
Message-ID: <20221207151153.GE1275553@chaop.bj.intel.com>
Reply-To: Chao Peng <chao.p.peng@linux.intel.com>
References: <20221202061347.1070246-1-chao.p.peng@linux.intel.com>
 <20221202061347.1070246-5-chao.p.peng@linux.intel.com>
 <CA+EHjTyzZ2n8kQxH_Qx72aRq1k+dETJXTsoOM3tggPZAZkYbCA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CA+EHjTyzZ2n8kQxH_Qx72aRq1k+dETJXTsoOM3tggPZAZkYbCA@mail.gmail.com>
Precedence: bulk

On Tue, Dec 06, 2022 at 03:47:20PM +0000, Fuad Tabba wrote:
> Hi,
> 
> On Fri, Dec 2, 2022 at 6:19 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> >
> > This new KVM exit allows userspace to handle memory-related errors. It
> > indicates an error happens in KVM at guest memory range [gpa, gpa+size).
> > The flags includes additional information for userspace to handle the
> > error. Currently bit 0 is defined as 'private memory' where '1'
> > indicates error happens due to private memory access and '0' indicates
> > error happens due to shared memory access.
> >
> > When private memory is enabled, this new exit will be used for KVM to
> > exit to userspace for shared <-> private memory conversion in memory
> > encryption usage. In such usage, typically there are two kind of memory
> > conversions:
> >   - explicit conversion: happens when guest explicitly calls into KVM
> >     to map a range (as private or shared), KVM then exits to userspace
> >     to perform the map/unmap operations.
> >   - implicit conversion: happens in KVM page fault handler where KVM
> >     exits to userspace for an implicit conversion when the page is in a
> >     different state than requested (private or shared).
> >
> > Suggested-by: Sean Christopherson <seanjc@google.com>
> > Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> > Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > Reviewed-by: Fuad Tabba <tabba@google.com>
> > ---
> >  Documentation/virt/kvm/api.rst | 22 ++++++++++++++++++++++
> >  include/uapi/linux/kvm.h       |  8 ++++++++
> >  2 files changed, 30 insertions(+)
> >
> > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> > index 99352170c130..d9edb14ce30b 100644
> > --- a/Documentation/virt/kvm/api.rst
> > +++ b/Documentation/virt/kvm/api.rst
> > @@ -6634,6 +6634,28 @@ array field represents return values. The userspace should update the return
> >  values of SBI call before resuming the VCPU. For more details on RISC-V SBI
> >  spec refer, https://github.com/riscv/riscv-sbi-doc.
> >
> > +::
> > +
> > +               /* KVM_EXIT_MEMORY_FAULT */
> > +               struct {
> > +  #define KVM_MEMORY_EXIT_FLAG_PRIVATE (1ULL << 0)
> > +                       __u64 flags;
> 
> I see you've removed the padding and increased the flag size.

Yes Sean suggested this and also looks good to me.

Chao
> 
> Reviewed-by: Fuad Tabba <tabba@google.com>
> Tested-by: Fuad Tabba <tabba@google.com>
> 
> Cheers,
> /fuad
> 
> 
> 
> 
> > +                       __u64 gpa;
> > +                       __u64 size;
> > +               } memory;
> > +
> > +If exit reason is KVM_EXIT_MEMORY_FAULT then it indicates that the VCPU has
> > +encountered a memory error which is not handled by KVM kernel module and
> > +userspace may choose to handle it. The 'flags' field indicates the memory
> > +properties of the exit.
> > +
> > + - KVM_MEMORY_EXIT_FLAG_PRIVATE - indicates the memory error is caused by
> > +   private memory access when the bit is set. Otherwise the memory error is
> > +   caused by shared memory access when the bit is clear.
> > +
> > +'gpa' and 'size' indicate the memory range the error occurs at. The userspace
> > +may handle the error and return to KVM to retry the previous memory access.
> > +
> >  ::
> >
> >      /* KVM_EXIT_NOTIFY */
> > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> > index 13bff963b8b0..c7e9d375a902 100644
> > --- a/include/uapi/linux/kvm.h
> > +++ b/include/uapi/linux/kvm.h
> > @@ -300,6 +300,7 @@ struct kvm_xen_exit {
> >  #define KVM_EXIT_RISCV_SBI        35
> >  #define KVM_EXIT_RISCV_CSR        36
> >  #define KVM_EXIT_NOTIFY           37
> > +#define KVM_EXIT_MEMORY_FAULT     38
> >
> >  /* For KVM_EXIT_INTERNAL_ERROR */
> >  /* Emulate instruction failed. */
> > @@ -541,6 +542,13 @@ struct kvm_run {
> >  #define KVM_NOTIFY_CONTEXT_INVALID     (1 << 0)
> >                         __u32 flags;
> >                 } notify;
> > +               /* KVM_EXIT_MEMORY_FAULT */
> > +               struct {
> > +#define KVM_MEMORY_EXIT_FLAG_PRIVATE   (1ULL << 0)
> > +                       __u64 flags;
> > +                       __u64 gpa;
> > +                       __u64 size;
> > +               } memory;
> >                 /* Fix the size of the union. */
> >                 char padding[256];
> >         };
> > --
> > 2.25.1
> >