linux-kernel - Re: [PATCH v5 07/13] KVM: Add KVM_EXIT_MEMORY

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Message-ID: <YkI3wa3rmWTOrpmw@google.com>
Date:   Mon, 28 Mar 2022 22:33:37 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Chao Peng <chao.p.peng@...ux.intel.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org, qemu-devel@...gnu.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
        ak@...ux.intel.com, david@...hat.com
Subject: Re: [PATCH v5 07/13] KVM: Add KVM_EXIT_MEMORY_ERROR exit

On Thu, Mar 10, 2022, Chao Peng 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.
> 
> After private memory is enabled, this new exit will be used for KVM to
> exit to userspace for shared memory <-> 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
>     do the map/unmap operations.
>   - implicit conversion: happens in KVM page fault handler.
>     * if the fault is due to a private memory access then causes a
>       userspace exit for a shared->private conversion request when the
>       page has not been allocated in the private memory backend.
>     * If the fault is due to a shared memory access then causes a
>       userspace exit for a private->shared conversion request when the
>       page has already been allocated in the private memory backend.
> 
> Signed-off-by: Yu Zhang <yu.c.zhang@...ux.intel.com>
> Signed-off-by: Chao Peng <chao.p.peng@...ux.intel.com>
> ---
>  Documentation/virt/kvm/api.rst | 22 ++++++++++++++++++++++
>  include/uapi/linux/kvm.h       |  9 +++++++++
>  2 files changed, 31 insertions(+)
> 
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index f76ac598606c..bad550c2212b 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -6216,6 +6216,28 @@ 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_ERROR */
> +		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_ERROR then it indicates that the VCPU has

Doh, I'm pretty sure I suggested KVM_EXIT_MEMORY_ERROR.  Any objection to using
KVM_EXIT_MEMORY_FAULT instead of KVM_EXIT_MEMORY_ERROR?  "ERROR" makes me think
of ECC errors, i.e. uncorrected #MC in x86 land, not more generic "faults".  That
would align nicely with -EFAULT.

> +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.