Re: [Xen-devel] [PATCH v2 1/2] x86/altp2m: use __get_gfn_type_access to avoid lock conflicts

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Wed, Aug 10, 2016 at 4:00 PM, Tamas K Lengyel
<tamas.lengyel@xxxxxxxxxxxx> wrote:
> From: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
>
> Use __get_gfn_type_access instead of get_gfn_type_access when checking
> the hostp2m entries during altp2m mem_access setting and gfn remapping
> to avoid a lock conflict which can make dom0 freeze. During mem_access
> setting the hp2m is already locked. For gfn remapping we change the flow
> to lock the hp2m before locking the ap2m.
>
> Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
> Reviewed-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>

Acked-by: George Dunlap <george.dunlap@xxxxxxxxxx>

> ---
> Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>
> v2: Lock the hp2m during gfn remapping
> ---
>  xen/arch/x86/mm/p2m.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
> index 812dbf6..1eeb934 100644
> --- a/xen/arch/x86/mm/p2m.c
> +++ b/xen/arch/x86/mm/p2m.c
> @@ -1787,8 +1787,8 @@ int p2m_set_altp2m_mem_access(struct domain *d, struct 
> p2m_domain *hp2m,
>      if ( !mfn_valid(mfn) )
>      {
>
> -        mfn = get_gfn_type_access(hp2m, gfn_l, &t, &old_a,
> -                                  P2M_ALLOC | P2M_UNSHARE, &page_order);
> +        mfn = __get_gfn_type_access(hp2m, gfn_l, &t, &old_a,
> +                                    P2M_ALLOC | P2M_UNSHARE, &page_order, 0);
>
>          rc = -ESRCH;
>          if ( !mfn_valid(mfn) || t != p2m_ram_rw )
> @@ -2548,6 +2548,7 @@ int p2m_change_altp2m_gfn(struct domain *d, unsigned 
> int idx,
>      hp2m = p2m_get_hostp2m(d);
>      ap2m = d->arch.altp2m_p2m[idx];
>
> +    p2m_lock(hp2m);
>      p2m_lock(ap2m);
>
>      mfn = ap2m->get_entry(ap2m, gfn_x(old_gfn), &t, &a, 0, NULL, NULL);
> @@ -2563,8 +2564,8 @@ int p2m_change_altp2m_gfn(struct domain *d, unsigned 
> int idx,
>      /* Check host p2m if no valid entry in alternate */
>      if ( !mfn_valid(mfn) )
>      {
> -        mfn = get_gfn_type_access(hp2m, gfn_x(old_gfn), &t, &a,
> -                                  P2M_ALLOC | P2M_UNSHARE, &page_order);
> +        mfn = __get_gfn_type_access(hp2m, gfn_x(old_gfn), &t, &a,
> +                                    P2M_ALLOC | P2M_UNSHARE, &page_order, 0);
>
>          if ( !mfn_valid(mfn) || t != p2m_ram_rw )
>              goto out;
> @@ -2606,6 +2607,7 @@ int p2m_change_altp2m_gfn(struct domain *d, unsigned 
> int idx,
>
>   out:
>      p2m_unlock(ap2m);
> +    p2m_unlock(hp2m);
>      return rc;
>  }
>
> --
> 2.8.1
>
>
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