Re: [Xen-devel] [PATCH v2 1/3] x86/mm: Introduce altp2m_get_gfn_type_access

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Mon, Apr 8, 2019 at 2:13 AM Alexandru Stefan ISAILA
<aisaila@xxxxxxxxxxxxxxx> wrote:
>
>
> On 05.04.2019 18:04, Tamas K Lengyel wrote:
> > On Fri, Apr 5, 2019 at 7:25 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>
> >> ---
> >>   xen/arch/x86/mm/mem_access.c | 30 +++++++++++------------------
> >>   xen/arch/x86/mm/p2m.c        | 37 ++++++++++++++----------------------
> >>   xen/include/asm-x86/p2m.h    | 23 ++++++++++++++++++++++
> >>   3 files changed, 48 insertions(+), 42 deletions(-)
> >>
> >> diff --git a/xen/arch/x86/mm/mem_access.c b/xen/arch/x86/mm/mem_access.c
> >> index 56c06a4fc6..608f748a57 100644
> >> --- a/xen/arch/x86/mm/mem_access.c
> >> +++ b/xen/arch/x86/mm/mem_access.c
> >> @@ -265,31 +265,23 @@ 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 found_in_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, 
> >> &found_in_hostp2m);
> >>
> >> -    /* Check host p2m if no valid entry in alternate */
> >>       if ( !mfn_valid(mfn) )
> >> -    {
> >> +        return -ESRCH;
> >>
> >> -        mfn = __get_gfn_type_access(hp2m, gfn_l, &t, &old_a,
> >> -                                    P2M_ALLOC | P2M_UNSHARE, &page_order, 
> >> 0);
> >> +    /* If this is a superpage, copy that first */
> >> +    if ( page_order != PAGE_ORDER_4K && found_in_hostp2m )
> >> +    {
> >> +        unsigned long mask = ~((1UL << page_order) - 1);
> >> +        gfn_t gfn2 = _gfn(gfn_l & mask);
> >> +        mfn_t mfn2 = _mfn(mfn_x(mfn) & mask);
> >>
> >> -        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..b2a5c0c42e 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 found_in_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, 
> >> &found_in_hostp2m);
> >>
> >>       if ( gfn_eq(new_gfn, INVALID_GFN) )
> >>       {
> >> @@ -2648,35 +2649,25 @@ 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, &page_order, 0);
> >> -
> >> -        if ( !mfn_valid(mfn) || t != p2m_ram_rw )
> >> -            goto out;
> >> +         goto out;
> >>
> >> -        /* If this is a superpage, copy that first */
> >> -        if ( page_order != PAGE_ORDER_4K )
> >> -        {
> >> -            gfn_t gfn;
> >> -            unsigned long mask;
> >> +    /* If this is a superpage, copy that first */
> >> +    if ( page_order != PAGE_ORDER_4K && found_in_hostp2m )
> >> +    {
> >> +        gfn_t gfn;
> >> +        unsigned long mask;
> >>
> >> -            mask = ~((1UL << page_order) - 1);
> >> -            gfn = _gfn(gfn_x(old_gfn) & mask);
> >> -            mfn = _mfn(mfn_x(mfn) & mask);
> >> +        mask = ~((1UL << page_order) - 1);
> >> +        gfn = _gfn(gfn_x(old_gfn) & mask);
> >> +        mfn = _mfn(mfn_x(mfn) & mask);
> >>
> >> -            if ( ap2m->set_entry(ap2m, gfn, mfn, page_order, t, a, 1) )
> >> -                goto out;
> >> -        }
> >> +        if ( ap2m->set_entry(ap2m, gfn, mfn, page_order, t, a, 1) )
> >> +            goto out;
> >>       }
> >>
> >> -    mfn = ap2m->get_entry(ap2m, new_gfn, &t, &a, 0, NULL, NULL);
> >> +    mfn = altp2m_get_gfn_type_access(ap2m, new_gfn, &t, &a, &page_order, 
> >> &found_in_hostp2m);
> >>
> >>       if ( !mfn_valid(mfn) )
> >> -        mfn = hp2m->get_entry(hp2m, new_gfn, &t, &a, 0, NULL, NULL);
> >> -
> >> -    /* Note: currently it is not safe to remap to a shared entry */
> >> -    if ( !mfn_valid(mfn) || (t != p2m_ram_rw) )
> >>           goto out;
> >>
> >>       if ( !ap2m->set_entry(ap2m, old_gfn, mfn, PAGE_ORDER_4K, t, a,
> >> diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
> >> index 2801a8ccca..42068b4aed 100644
> >> --- a/xen/include/asm-x86/p2m.h
> >> +++ b/xen/include/asm-x86/p2m.h
> >> @@ -448,6 +448,29 @@ static inline mfn_t __nonnull(3) get_gfn_type(
> >>       return get_gfn_type_access(p2m_get_hostp2m(d), gfn, t, &a, q, NULL);
> >>   }
> >>
> >> +static inline mfn_t altp2m_get_gfn_type_access(
> >> +    struct p2m_domain *ap2m, gfn_t gfn, p2m_type_t *t, p2m_access_t *a,
> >> +    unsigned int *page_order, bool *found_in_hostp2m)
> >
> > I don't like this. The way it's implemented is very convoluted and not
> > consistent.
> >
> >> +{
> >> +    mfn_t mfn = ap2m->get_entry(ap2m, gfn, t, a, 0, NULL, NULL);
> >> +
> >> +    *found_in_hostp2m = false;
> >
> > Just because an entry is in the altp2m now means it's not found in the
> > hostp2m? Doesn't make sense.
>
> The name of the var is not a good one I must agree. I tried to
> incorporate as much as the common code in one function.
>
> The found_in_hostp2m var is used by the caller in the page_order !=
> PAGE_ORDER_4K case.
>
> >
> >> +
> >> +    /* Check host p2m if no valid entry in alternate */
> >> +    if ( !mfn_valid(mfn) )
> >> +    {
> >> +        mfn = __get_gfn_type_access(p2m_get_hostp2m(ap2m->domain), 
> >> gfn_x(gfn), t, a,
> >> +                                    P2M_ALLOC | P2M_UNSHARE, page_order, 
> >> false);
> >> +        *found_in_hostp2m = true;
> >
> > Now it's found in the hostp2m, even if the mfn is invalid? Again,
> > doesn't make sense.
>
> I agree that the true comes here early and it can get true only if mfn
> is valid.
>
> >
> >> +
> >> +        /* Note: currently it is not safe to remap to a shared entry */
> >> +        if ( !mfn_valid(mfn) || *t != p2m_ram_rw )
> >> +            return INVALID_MFN;
> >
> > This function is supposed to just get the type and access.. but
> > instead it does sanity checks on the results that the caller is
> > probably in a better position to judge. Again, inconsistent with the
> > function's name and seemingly intended use.
> >
>
> Ok I will get the check out of the function and let the caller.
>
> About the found_in_hostp2m var, should it get a different name?

It should reflect what it actually contains, which right now looks
like more like "copied_from_hostp2m".

Tamas

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel