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References: <20221025151344.3784230-1-chao.p.peng@linux.intel.com> <20221025151344.3784230-4-chao.p.peng@linux.intel.com>
In-Reply-To: <20221025151344.3784230-4-chao.p.peng@linux.intel.com>
From:   Fuad Tabba <tabba@google.com>
Date:   Thu, 27 Oct 2022 11:27:05 +0100
Message-ID: <CA+EHjTxzLDAW=MyfKFcL2cGQimw3bdVYePUgRw+=1+AbCQouUQ@mail.gmail.com>
Subject: Re: [PATCH v9 3/8] KVM: Add KVM_EXIT_MEMORY_FAULT exit
To:     Chao Peng <chao.p.peng@linux.intel.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>,
        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>,
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        Quentin Perret <qperret@google.com>,
        Michael Roth <michael.roth@amd.com>, mhocko@suse.com,
        Muchun Song <songmuchun@bytedance.com>, wei.w.wang@intel.com
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Hi,

On Tue, Oct 25, 2022 at 4:19 PM 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>

I have tested the V8 version of this patch on arm64/qemu, and
considering this hasn't changed:
Tested-by: Fuad Tabba <tabba@google.com>

Cheers,
/fuad


>  Documentation/virt/kvm/api.rst | 23 +++++++++++++++++++++++
>  include/uapi/linux/kvm.h       |  9 +++++++++
>  2 files changed, 32 insertions(+)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index f3fa75649a78..975688912b8c 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -6537,6 +6537,29 @@ 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 (1 << 0)
> +                       __u32 flags;
> +                       __u32 padding;
> +                       __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 f1ae45c10c94..fa60b032a405 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. */
> @@ -538,6 +539,14 @@ struct kvm_run {
>  #define KVM_NOTIFY_CONTEXT_INVALID     (1 << 0)
>                         __u32 flags;
>                 } notify;
> +               /* KVM_EXIT_MEMORY_FAULT */
> +               struct {
> +#define KVM_MEMORY_EXIT_FLAG_PRIVATE   (1 << 0)
> +                       __u32 flags;
> +                       __u32 padding;
> +                       __u64 gpa;
> +                       __u64 size;
> +               } memory;
>                 /* Fix the size of the union. */
>                 char padding[256];
>         };
> --
> 2.25.1
>