Re: [PATCH v10 4/9] KVM: Add KVM_EXIT_MEMORY_FAULT exit

[Fuad Tabba]

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.

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
>