Hi Stefano,
On 05/04/2022 22:50, Stefano Stabellini wrote:
+static void __init setup_mm(void)
+{
+ const struct meminfo *banks = &bootinfo.mem;
+ paddr_t ram_start = ~0;
+ paddr_t ram_end = 0;
+ paddr_t ram_size = 0;
+ unsigned int i;
+
+ init_pdx();
+
+ /*
+ * We need some memory to allocate the page-tables used for the xenheap
+ * mappings. But some regions may contain memory already allocated
+ * for other uses (e.g. modules, reserved-memory...).
+ *
+ * For simplify add all the free regions in the boot allocator.
+ */
We currently have:
BUG_ON(nr_bootmem_regions == (PAGE_SIZE / sizeof(struct bootmem_region)));
This has enough space for 256 distinct regions on arm64 (512 regions on
arm32).
Do you think we should check for the limit in populate_boot_allocator?
This patch doesn't change the number of regions added to the boot
allocator. So if we need to check the limit then I would rather deal
separately (see more below).
Or there is no need because it is unrealistic to reach it?
I can't say never because history told us on some UEFI systems, there
will be a large number of regions exposed. I haven't heard anyone that
would hit the BUG_ON().
The problem is what do we do if we hit the limit? We could ignore all
the regions after. However, there are potentially a risk there would not
be enough memory to cover the boot memory allocation (regions may be
really small).
So if we ever hit the limit, then I think we should update the boot
allocator.
Cheers,
--
Julien Grall
