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 8:48 AM Alexandru Stefan ISAILA
<aisaila@xxxxxxxxxxxxxxx> wrote:
>
>
>
> On 09.04.2019 17:37, Tamas K Lengyel wrote:
> > 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?
>
> The (t != p2m_ram_rw) check was done only for the get from hostp2m.
>
> If you think that I should do the check for all mfns (hostp2 and altp2m)
> then I can drop the copied_from_hostp2m bool and add mmio check.

I think you should just drop the && copied_from_hostp2m part of it.
Remappings should only be allowed for p2m_ram_rw type, no matter which
p2m its coming from.

Tamas

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