On 07/01/2020 16:30, Jan Beulich wrote:
>>> for ( i = 0; i < 8; ++i )
>>> {
>>> unsigned int slot = (xen_phys_start >> L2_PAGETABLE_SHIFT) + i;
>>> paddr_t addr = slot << L2_PAGETABLE_SHIFT;
>>>
>>> l2_identmap[slot] = l2e_from_paddr(addr,
>>> PAGE_HYPERVISOR|_PAGE_PSE);
>>> - slot &= L2_PAGETABLE_ENTRIES - 1;
>>> l2_bootmap[slot] = l2e_from_paddr(addr,
>>> __PAGE_HYPERVISOR|_PAGE_PSE);
>>> }
>>> - /* Initialise L3 boot-map page directory entries. */
>>> - l3_bootmap[l3_table_offset(xen_phys_start)] =
>>> - l3e_from_paddr((UINTN)l2_bootmap, __PAGE_HYPERVISOR);
>>> - l3_bootmap[l3_table_offset(xen_phys_start + (8 << L2_PAGETABLE_SHIFT)
>>> - 1)] =
>>> - l3e_from_paddr((UINTN)l2_bootmap, __PAGE_HYPERVISOR);
>>> +
>>> + /* Initialize L3 boot-map page directory entries. */
>>> + for ( i = 0; i < 4; ++i )
>>> + l3_bootmap[i] = l3e_from_paddr((UINTN)l2_bootmap + i * PAGE_SIZE,
>>> + __PAGE_HYPERVISOR);
>> The idea behind the original code was to be immune to the number
>> of pages l2_bootmap[] covers, as long as it's at least one (which
>> it'll always be, I would say). The minimum requirement to any
>> change to this I have is that the build must break if the size
>> assumption here is violated. I.e. there may not be a literal 4 as
>> the upper loop bound here, or there would need to be a
>> BUILD_BUG_ON() right next to it. But I'd really prefer if the
>> code was left as is (perhaps with a comment added), unless you
>> can point out actual issues with it (which I can't see in the
>> description), or you can otherwise justify the change with better
>> than "the EFI side is further complicated by spraying non-identity
>> aliases into the mix."
> And if this change is to be made, won't it mean the code in setup.c
> commented with "Make boot page tables match non-EFI boot" can then
> go away at the same time?
When I've figured out why altering that causes the EFI boot to fail, yes
- that was the plan...
~Andrew
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel
