Re: [Xen-devel] [PATCH V5] x86/ioreq_server: Make p2m_finish_type_change actually work

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On Sat, May 13, 2017 at 1:34 AM, Xiong Zhang <xiong.y.zhang@xxxxxxxxx> wrote:
> Commit 6d774a951696 ("x86/ioreq server: synchronously reset outstanding
> p2m_ioreq_server entries when an ioreq server unmaps") introduced
> p2m_finish_type_change(), which was meant to synchronously finish a
> previously initiated type change over a gpfn range.  It did this by
> calling get_entry(), checking if it was the appropriate type, and then
> calling set_entry().
>
> Unfortunately, a previous commit (1679e0df3df6 "x86/ioreq server:
> asynchronously reset outstanding p2m_ioreq_server entries") modified
> get_entry() to always return the new type after the type change, meaning
> that p2m_finish_type_change() never changed any entries.  Which means
> when an ioreq server was detached and then re-attached (as happens in
> XenGT on reboot) the re-attach failed.
>
> Fix this by using the existing p2m-specific recalculation logic instead
> of doing a read-check-write loop.
>
> Fix: 'commit 6d774a951696 ("x86/ioreq server: synchronously reset
>       outstanding p2m_ioreq_server entries when an ioreq server unmaps")'
>
> Signed-off-by: Xiong Zhang <xiong.y.zhang@xxxxxxxxx>
> Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
> Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> v1: Add ioreq_pre_recalc query flag to get the old p2m_type.(Jan)
> v2: Add p2m->recalc() hook to change gfn p2m_type. (George)
> v3: Make commit message clearer. (George)
>     Keep the name of p2m-specific recal function unchanged. (Jan)
> v4: Move version info below S-o-B and handle return value of
>     p2m->recalc. (Jan)
> v5: Fix coding style. (Julien)
>
> The target of this patch is Xen 4.9.
> ---
>  xen/arch/x86/hvm/dm.c     |  5 +++--
>  xen/arch/x86/mm/p2m-ept.c |  1 +
>  xen/arch/x86/mm/p2m-pt.c  |  1 +
>  xen/arch/x86/mm/p2m.c     | 35 +++++++++++++++++++++++------------
>  xen/include/asm-x86/p2m.h |  9 +++++----
>  5 files changed, 33 insertions(+), 18 deletions(-)
>
> diff --git a/xen/arch/x86/hvm/dm.c b/xen/arch/x86/hvm/dm.c
> index d72b7bd..99bf66a 100644
> --- a/xen/arch/x86/hvm/dm.c
> +++ b/xen/arch/x86/hvm/dm.c
> @@ -412,8 +412,9 @@ static int dm_op(domid_t domid,
>                      first_gfn <= p2m->max_mapped_pfn )
>              {
>                  /* Iterate p2m table for 256 gfns each time. */
> -                p2m_finish_type_change(d, _gfn(first_gfn), 256,
> -                                       p2m_ioreq_server, p2m_ram_rw);
> +                rc = p2m_finish_type_change(d, _gfn(first_gfn), 256);
> +                if ( rc < 0 )
> +                    break;
>
>                  first_gfn += 256;
>
> diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
> index f37a1f2..09efba7 100644
> --- a/xen/arch/x86/mm/p2m-ept.c
> +++ b/xen/arch/x86/mm/p2m-ept.c
> @@ -1238,6 +1238,7 @@ int ept_p2m_init(struct p2m_domain *p2m)
>
>      p2m->set_entry = ept_set_entry;
>      p2m->get_entry = ept_get_entry;
> +    p2m->recalc = resolve_misconfig;
>      p2m->change_entry_type_global = ept_change_entry_type_global;
>      p2m->change_entry_type_range = ept_change_entry_type_range;
>      p2m->memory_type_changed = ept_memory_type_changed;
> diff --git a/xen/arch/x86/mm/p2m-pt.c b/xen/arch/x86/mm/p2m-pt.c
> index 5079b59..2eddeee 100644
> --- a/xen/arch/x86/mm/p2m-pt.c
> +++ b/xen/arch/x86/mm/p2m-pt.c
> @@ -1153,6 +1153,7 @@ void p2m_pt_init(struct p2m_domain *p2m)
>  {
>      p2m->set_entry = p2m_pt_set_entry;
>      p2m->get_entry = p2m_pt_get_entry;
> +    p2m->recalc = do_recalc;
>      p2m->change_entry_type_global = p2m_pt_change_entry_type_global;
>      p2m->change_entry_type_range = p2m_pt_change_entry_type_range;
>      p2m->write_p2m_entry = paging_write_p2m_entry;
> diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
> index 1d57e5c..1600422 100644
> --- a/xen/arch/x86/mm/p2m.c
> +++ b/xen/arch/x86/mm/p2m.c
> @@ -1011,33 +1011,44 @@ void p2m_change_type_range(struct domain *d,
>      p2m_unlock(p2m);
>  }
>
> -/* Synchronously modify the p2m type for a range of gfns from ot to nt. */
> -void p2m_finish_type_change(struct domain *d,
> -                            gfn_t first_gfn, unsigned long max_nr,
> -                            p2m_type_t ot, p2m_type_t nt)
> +/*
> + * Finish p2m type change for gfns which are marked as need_recalc in a 
> range.
> + * Returns: 0/1 for success, negative for failure
> + */
> +int p2m_finish_type_change(struct domain *d,
> +                           gfn_t first_gfn, unsigned long max_nr)
>  {
>      struct p2m_domain *p2m = p2m_get_hostp2m(d);
> -    p2m_type_t t;
>      unsigned long gfn = gfn_x(first_gfn);
>      unsigned long last_gfn = gfn + max_nr - 1;
> -
> -    ASSERT(ot != nt);
> -    ASSERT(p2m_is_changeable(ot) && p2m_is_changeable(nt));
> +    int rc = 0;
>
>      p2m_lock(p2m);
>
>      last_gfn = min(last_gfn, p2m->max_mapped_pfn);
>      while ( gfn <= last_gfn )
>      {
> -        get_gfn_query_unlocked(d, gfn, &t);
> -
> -        if ( t == ot )
> -            p2m_change_type_one(d, gfn, t, nt);
> +        rc = p2m->recalc(p2m, gfn);
> +        /*
> +         * ept->recalc could return 0/1/-ENOMEM. pt->recalc could return
> +         * 0/-ENOMEM/-ENOENT, -ENOENT isn't an error as we are looping
> +         * gfn here.
> +         */

Hmm, now that these functions are being called externally it would be
good if their semantics was the same.  But since we're a bit late in
the cycle to do that kind of rework:

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

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