Re: [PATCH 3/3] x86/mem_sharing: make fork_reset more configurable

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Mar 22, 2022 at 01:41:39PM -0400, Tamas K Lengyel wrote:
> diff --git a/xen/include/public/memory.h b/xen/include/public/memory.h
> index 208d8dcbd9..30ce23c5a7 100644
> --- a/xen/include/public/memory.h
> +++ b/xen/include/public/memory.h
> @@ -541,12 +541,14 @@ struct xen_mem_sharing_op {
>                  uint32_t gref;     /* IN: gref to debug         */
>              } u;
>          } debug;
> -        struct mem_sharing_op_fork {      /* OP_FORK */
> +        struct mem_sharing_op_fork {      /* OP_FORK/_RESET */
>              domid_t parent_domain;        /* IN: parent's domain id */
>  /* These flags only makes sense for short-lived forks */
>  #define XENMEM_FORK_WITH_IOMMU_ALLOWED (1u << 0)
>  #define XENMEM_FORK_BLOCK_INTERRUPTS   (1u << 1)
>  #define XENMEM_FORK_SKIP_SPECIAL_PAGES (1u << 2)
> +#define XENMEM_FORK_RESET_STATE        (1u << 3)
> +#define XENMEM_FORK_RESET_MEMORY       (1u << 4)
>              uint16_t flags;               /* IN: optional settings */
>              uint32_t pad;                 /* Must be set to 0 */
>          } fork;
> diff --git a/xen/include/public/vm_event.h b/xen/include/public/vm_event.h
> index bb003d21d0..81c2ee28cc 100644
> --- a/xen/include/public/vm_event.h
> +++ b/xen/include/public/vm_event.h
> @@ -127,6 +127,14 @@
>   * Reset the vmtrace buffer (if vmtrace is enabled)
>   */
>  #define VM_EVENT_FLAG_RESET_VMTRACE      (1 << 13)
> +/*
> + * Reset the VM state (if VM is fork)
> + */
> +#define VM_EVENT_FLAG_RESET_FORK_STATE   (1 << 14)
> +/*
> + * Remove unshared entried from physmap (if VM is fork)
> + */
> +#define VM_EVENT_FLAG_RESET_FORK_MEMORY  (1 << 15)

I'm confused about why two different interfaces are added to do this
kind of selective resets, one to vm_event and one to xenmem_fork?

I thin k the natural place for the option to live would be
XENMEM_FORK?

Thanks, Roger.