On 4/4/25 9:52 AM, Jan Beulich wrote:
On 04.04.2025 09:31, Oleksii Kurochko wrote:
On 4/4/25 8:56 AM, Jan Beulich wrote:
On 03.04.2025 18:20, Oleksii Kurochko wrote:
On 4/1/25 6:04 PM, Jan Beulich wrote:
On 01.04.2025 17:58, Oleksii Kurochko wrote:
On 3/31/25 6:14 PM, Jan Beulich wrote:
On 31.03.2025 17:20, Oleksii Kurochko wrote:
+ _AC(XEN_VIRT_START, UL) >> vpn1_shift;
+ const unsigned long xen_virt_end_vpn =
+ xen_virt_starn_vpn + ((XEN_VIRT_SIZE >> vpn1_shift) - 1);
+
if ((va >= DIRECTMAP_VIRT_START) &&
(va <= DIRECTMAP_VIRT_END))
return directmapoff_to_maddr(va - directmap_virt_start);
- BUILD_BUG_ON(XEN_VIRT_SIZE != MB(2));
- ASSERT((va >> (PAGETABLE_ORDER + PAGE_SHIFT)) ==
- (_AC(XEN_VIRT_START, UL) >> (PAGETABLE_ORDER + PAGE_SHIFT)));
+ BUILD_BUG_ON(XEN_VIRT_SIZE != MB(8));
Is it necessary to be != ? Won't > suffice?
It could be just > MB(2). Or perphaps >=.
= would make the build fail, wouldn't it?
I just realized that BUILD_BUG_ON() condition is compared to zero so actually
everything what
will make the condition true will cause a build fail as inside it used
!(condition).
???
|BUILD_BUG_ON()| forces a compilation error if the given condition is true.
Therefore, if the condition
|XEN_VIRT_SIZE != MB(2)| is changed to|XEN_VIRT_SIZE > MB(2)|, the condition
will always evaluate to true
(assuming|XEN_VIRT_SIZE| is greater than 2 MB), which will result in a
compilation error.
Well, it was you who used MB(2) in a reply, when previously talk was of MB(8),
and that to grow to MB(16). The BUILD_BUG_ON() is - aiui - about you having set
aside enough page table space. Quite possibly the need for this BUILD_BUG_ON()
then disappears altogether when XEN_VIRT_SIZE is properly taken into account
for the number-of-page-tables calculation. In no event do I see why the MB(2)
boundary would be relevant for anything going forward.
Also, doesn’t|BUILD_BUG_ON()| affect how the|ASSERT()| that follows it is
written?
The changes, at the moment, look like:
+ const unsigned int vpn1_shift = PAGETABLE_ORDER + PAGE_SHIFT;
+ const unsigned long va_vpn = va >> vpn1_shift;
+ const unsigned long xen_virt_start_vpn =
+ _AC(XEN_VIRT_START, UL) >> vpn1_shift;
+ const unsigned long xen_virt_end_vpn =
+ xen_virt_start_vpn + ((XEN_VIRT_SIZE >> vpn1_shift) - 1);
+
if ((va >= DIRECTMAP_VIRT_START) &&
(va <= DIRECTMAP_VIRT_END))
return directmapoff_to_maddr(va - directmap_virt_start);
- BUILD_BUG_ON(XEN_VIRT_SIZE != MB(2));
- ASSERT((va >> (PAGETABLE_ORDER + PAGE_SHIFT)) ==
- (_AC(XEN_VIRT_START, UL) >> (PAGETABLE_ORDER + PAGE_SHIFT)));
+ BUILD_BUG_ON(XEN_VIRT_SIZE != MB(16));
+ ASSERT((va_vpn >= xen_virt_start_vpn) && (va_vpn <= xen_virt_end_vpn));
If|XEN_VIRT_SIZE| is greater than|GB(1)|, then|xen_virt_end_vpn| may be
calculated
incorrectly.
For example, if|XEN_VIRT_START| is|0xFFFFFFFF80000000| and|XEN_VIRT_SIZE|
is|0x40200000|,
then|(XEN_VIRT_SIZE >> vpn1_shift)| equals 513, whereas|va_vpn| is always in
the range [0, 511],
but xen_virt_end_vpn will be greater then 511.
So shouldn't it be checked before ASSERT() that XEN_VIRT_SIZE is <= GB(1):
BUILD_BUG_ON(XEN_VIRT_SIZE <= GB(1))?
~ Oleksii
