Re: [PATCH for-4.15] x86/mem_sharing: copy parent VM's hostp2m's max_mapped_pfn during forking

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Thu, Mar 18, 2021 at 5:36 PM Tamas K Lengyel <tamas.lengyel@xxxxxxxxx> wrote:
>
> When creating a VM fork copy the parent VM's hostp2m max_mapped_pfn value. 
> Some
> toolstack relies on the XENMEM_maximum_gpfn value to establish the maximum
> addressable physical memory in the VM and for forks that have not yet been
> unpaused that value is not going to reflect the correct max gpfn that's
> possible to populate into the p2m. This patch fixes the issue.
>
> Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxx>
> ---
>  xen/arch/x86/mm/mem_sharing.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
> index 00ada05c10..98b14f7b0a 100644
> --- a/xen/arch/x86/mm/mem_sharing.c
> +++ b/xen/arch/x86/mm/mem_sharing.c
> @@ -1761,6 +1761,7 @@ static int copy_settings(struct domain *cd, struct 
> domain *d)
>          return rc;
>
>      copy_tsc(cd, d);
> +    p2m_get_hostp2m(cd)->max_mapped_pfn = p2m_get_hostp2m(d)->max_mapped_pfn;
>
>      return rc;
>  }
> --
> 2.25.1
>

CC-ing Ian as 4.15 release manager. This patch is safe to include in
4.15 as it's a minor fix in a tech preview feature that's not even
compiled by default.

Thanks,
Tamas