Re: [Xen-devel] [PATCH v3 1/3] x86/mm: Introduce altp2m_get_gfn_type_access

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Tue, Apr 9, 2019 at 8:03 AM Alexandru Stefan ISAILA
<aisaila@xxxxxxxxxxxxxxx> wrote:
>
>
>
> On 09.04.2019 16:48, Tamas K Lengyel wrote:
> > On Tue, Apr 9, 2019 at 6:04 AM Alexandru Stefan ISAILA
> > <aisaila@xxxxxxxxxxxxxxx> wrote:
> >>
> >> This patch moves common code from p2m_set_altp2m_mem_access() and
> >> p2m_change_altp2m_gfn() into one function
> >>
> >> Signed-off-by: Alexandru Isaila <aisaila@xxxxxxxxxxxxxxx>
> >>
> >> ---
> >> Changes since V2:
> >>          - Change var name from found_in_hostp2m to copied_from_hostp2m
> >>          - Move the type check from altp2m_get_gfn_type_access() to the
> >>          callers.
> >> ---
> >>   xen/arch/x86/mm/mem_access.c | 32 ++++++++++++----------------
> >>   xen/arch/x86/mm/p2m.c        | 41 ++++++++++++++----------------------
> >>   xen/include/asm-x86/p2m.h    | 19 +++++++++++++++++
> >>   3 files changed, 49 insertions(+), 43 deletions(-)
> >>
> >> diff --git a/xen/arch/x86/mm/mem_access.c b/xen/arch/x86/mm/mem_access.c
> >> index 56c06a4fc6..bf67ddb15a 100644
> >> --- a/xen/arch/x86/mm/mem_access.c
> >> +++ b/xen/arch/x86/mm/mem_access.c
> >> @@ -265,31 +265,27 @@ int p2m_set_altp2m_mem_access(struct domain *d, 
> >> struct p2m_domain *hp2m,
> >>       unsigned int page_order;
> >>       unsigned long gfn_l = gfn_x(gfn);
> >>       int rc;
> >> +    bool copied_from_hostp2m;
> >>
> >> -    mfn = ap2m->get_entry(ap2m, gfn, &t, &old_a, 0, NULL, NULL);
> >> +    mfn = altp2m_get_gfn_type_access(ap2m, gfn, &t, &old_a, &page_order, 
> >> &copied_from_hostp2m);
> >>
> >> -    /* Check host p2m if no valid entry in alternate */
> >>       if ( !mfn_valid(mfn) )
> >> +        return -ESRCH;
> >> +
> >> +    /* If this is a superpage, copy that first */
> >> +    if ( page_order != PAGE_ORDER_4K && copied_from_hostp2m )
> >>       {
> >> +        unsigned long mask = ~((1UL << page_order) - 1);
> >> +        gfn_t gfn2 = _gfn(gfn_l & mask);
> >> +        mfn_t mfn2 = _mfn(mfn_x(mfn) & mask);
> >>
> >> -        mfn = __get_gfn_type_access(hp2m, gfn_l, &t, &old_a,
> >> -                                    P2M_ALLOC | P2M_UNSHARE, &page_order, 
> >> 0);
> >> +        /* Note: currently it is not safe to remap to a shared entry */
> >> +        if ( t != p2m_ram_rw )
> >> +            return -ESRCH;
> >>
> >> -        rc = -ESRCH;
> >> -        if ( !mfn_valid(mfn) || t != p2m_ram_rw )
> >> +        rc = ap2m->set_entry(ap2m, gfn2, mfn2, page_order, t, old_a, 1);
> >> +        if ( rc )
> >>               return rc;
> >> -
> >> -        /* If this is a superpage, copy that first */
> >> -        if ( page_order != PAGE_ORDER_4K )
> >> -        {
> >> -            unsigned long mask = ~((1UL << page_order) - 1);
> >> -            gfn_t gfn2 = _gfn(gfn_l & mask);
> >> -            mfn_t mfn2 = _mfn(mfn_x(mfn) & mask);
> >> -
> >> -            rc = ap2m->set_entry(ap2m, gfn2, mfn2, page_order, t, old_a, 
> >> 1);
> >> -            if ( rc )
> >> -                return rc;
> >> -        }
> >>       }
> >>
> >>       /*
> >> diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
> >> index b9bbb8f485..d38d7c29ca 100644
> >> --- a/xen/arch/x86/mm/p2m.c
> >> +++ b/xen/arch/x86/mm/p2m.c
> >> @@ -2626,6 +2626,7 @@ int p2m_change_altp2m_gfn(struct domain *d, unsigned 
> >> int idx,
> >>       mfn_t mfn;
> >>       unsigned int page_order;
> >>       int rc = -EINVAL;
> >> +    bool copied_from_hostp2m;
> >>
> >>       if ( idx >= MAX_ALTP2M || d->arch.altp2m_eptp[idx] == 
> >> mfn_x(INVALID_MFN) )
> >>           return rc;
> >> @@ -2636,7 +2637,7 @@ int p2m_change_altp2m_gfn(struct domain *d, unsigned 
> >> int idx,
> >>       p2m_lock(hp2m);
> >>       p2m_lock(ap2m);
> >>
> >> -    mfn = ap2m->get_entry(ap2m, old_gfn, &t, &a, 0, NULL, NULL);
> >> +    mfn = altp2m_get_gfn_type_access(ap2m, old_gfn, &t, &a, &page_order, 
> >> &copied_from_hostp2m);
> >>
> >>       if ( gfn_eq(new_gfn, INVALID_GFN) )
> >>       {
> >> @@ -2646,37 +2647,27 @@ int p2m_change_altp2m_gfn(struct domain *d, 
> >> unsigned int idx,
> >>           goto out;
> >>       }
> >>
> >> -    /* 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, &page_order, 0);
> >> +    if ( !mfn_valid(mfn) || (t != p2m_ram_rw && copied_from_hostp2m) )
> >
> > Is this check correct? Why do you want to get out only when type is
> > non-rw *and* it's copied from the hostp2m? You could have non-rw
> > entries like mmio in the altp2m that were lazily copied and I don't
> > think we want to allow remapping to those either.
>
> I just copied the functionality. If this is needed I will add a || t !=
> p2m_mmio_dm and p2m_mmio_direct.

My problem is with the && copied_form_hostp2m part. Why is that a criteria?

Tamas

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