Hi,
On 26/03/2020 09:09, Jan Beulich wrote:
On 25.03.2020 19:21, Julien Grall wrote:
On 25/03/2020 15:27, Jan Beulich wrote:
On 22.03.2020 17:14, jul...@xen.org wrote:
@@ -785,21 +781,21 @@ bool is_iomem_page(mfn_t mfn)
return (page_get_owner(page) == dom_io);
}
-static int update_xen_mappings(unsigned long mfn, unsigned int cacheattr)
+static int update_xen_mappings(mfn_t mfn, unsigned int cacheattr)
{
int err = 0;
- bool alias = mfn >= PFN_DOWN(xen_phys_start) &&
- mfn < PFN_UP(xen_phys_start + xen_virt_end - XEN_VIRT_START);
+ bool alias = mfn_x(mfn) >= PFN_DOWN(xen_phys_start) &&
+ mfn_x(mfn) < PFN_UP(xen_phys_start + xen_virt_end - XEN_VIRT_START);
unsigned long xen_va =
- XEN_VIRT_START + ((mfn - PFN_DOWN(xen_phys_start)) << PAGE_SHIFT);
+ XEN_VIRT_START + mfn_to_maddr(mfn_add(mfn, -PFN_DOWN(xen_phys_start)));
Depending on the types involved (e.g. in PFN_DOWN()) this may
or may not be safe, so I consider such a transformation at
least fragile. I think we either want to gain mfn_sub() or
keep this as a "real" subtraction.
I want to avoid mfn_x() as much as possible when everything can
be done using typesafe operation. But i am not sure how
mfn_sub() would solve the problem. Do you mind providing more
information?
Consider PFN_DOWN() potentially returning "unsigned int". The
negation of an unsigned int is still an unsigned int, and hence
e.g. -1U (which might result here) is really 0xFFFFFFFF rather
than -1L / -1UL as intended. Whereas with mfn_sub() the
conversion to unsigned long of the (positive) value to subtract
would occur as part of evaluating function arguments, and the
resulting subtraction would then be correct.
I will have a look to introduce mfn_sub().
@@ -584,21 +584,21 @@ static unsigned long init_node_heap(int node, unsigned
long mfn,
needed = 0;
}
else if ( *use_tail && nr >= needed &&
- arch_mfn_in_directmap(mfn + nr) &&
+ arch_mfn_in_directmap(mfn_x(mfn_add(mfn, nr))) &&
(!xenheap_bits ||
- !((mfn + nr - 1) >> (xenheap_bits - PAGE_SHIFT))) )
+ !((mfn_x(mfn) + nr - 1) >> (xenheap_bits - PAGE_SHIFT))) )
May I suggest consistency here: This one uses +, while ...
{
- _heap[node] = mfn_to_virt(mfn + nr - needed);
- avail[node] = mfn_to_virt(mfn + nr - 1) +
+ _heap[node] = mfn_to_virt(mfn_add(mfn, nr - needed));
+ avail[node] = mfn_to_virt(mfn_add(mfn, nr - 1)) +
PAGE_SIZE - sizeof(**avail) * NR_ZONES;
}
else if ( nr >= needed &&
- arch_mfn_in_directmap(mfn + needed) &&
+ arch_mfn_in_directmap(mfn_x(mfn_add(mfn, needed))) &&
... this one uses mfn_add() despite the mfn_x() around it, and ...
So the reason I used mfn_x(mfn_add(mfn, needed)) here is I plan
to convert arch_mfn_in_directmap() to use typesafe soon. In the
two others cases...
(!xenheap_bits ||
- !((mfn + needed - 1) >> (xenheap_bits - PAGE_SHIFT))) )
+ !((mfn_x(mfn) + needed - 1) >> (xenheap_bits - PAGE_SHIFT))) )
... here you use + again. My personal preference would be to avoid
constructs like mfn_x(mfn_add()).
... I am still unsure how to avoid mfn_x(). Do you have any ideas?
I don't see how it can be avoided right now. But I also don't see
why - for consistency, as said - you couldn't use mfn_x() also in
the middle case. You could then still convert to mfn_add() with
that future change of yours.
I could have as I could also have converted arch_mfn_in_directmap() to
use typesafe MFN. Anything around typesafe is a can of worms and this is
the fine line I found.
Anyway, I could not be bother to bikeshed... So I going to switch the
other one to mfn_x(...) + needed.
--- a/xen/include/asm-x86/mm.h
+++ b/xen/include/asm-x86/mm.h
@@ -667,7 +667,7 @@ static inline bool arch_mfn_in_directmap(unsigned long mfn)
{
unsigned long eva = min(DIRECTMAP_VIRT_END, HYPERVISOR_VIRT_END);
- return mfn <= (virt_to_mfn(eva - 1) + 1);
+ return mfn <= mfn_x(mfn_add(virt_to_mfn(eva - 1), 1));
Even if you wanted to stick to using mfn_add() here, there's one
blank too many after the comma.
I will remove the extra blank. Regarding the construction, I have
been wondering for a couple of years now whether we should
introduce mfn_{lt, gt}. What do you think?
I too have been wondering, and wouldn't mind their introduction
(plus mfn_le / mfn_ge perhaps). But it'll truly help you here
anyway only once the function parameter is also mfn_t.
This is a longer term plan. So I am going to leave it like that for now
until I manage to find time.
Cheers,
--
Julien Grall