On Thu, May 08 2014 at 6:25:29 pm BST, Mario Smarduch <m.smarduch@xxxxxxxxxxx> wrote:
> On 05/08/2014 10:12 AM, Marc Zyngier wrote:
>> On Thu, May 08 2014 at 6:03:07 pm BST, Mario Smarduch <m.smarduch@xxxxxxxxxxx> wrote:
>>> It appears that for a memslot that crosses a PUD range unmap_range may
>>> return prematurely if lower pud is not mapping anything.
>>>
>>> kvm_pud_addr_end(..) will return end and the loop will terminate possibly
>>> leaving unmapped ranges.
>>>
>>> Am I missing something?
>>
>> With 3-level page tables (which is what we have with LPAE on ARMv7),
>> puds are the same thing as pgds (they are effectively collapsed). This
>> will change with the introduction of 4-level page tables on ARMv8.
>>
>> M.
>>
>
> But what if there is some memslot with range like
> 0xffff0000 - 0x1000f0000. The lower range has not paged anything
> in so its pud/pgd is none, but upper range has mappings.
> Then pud_none(...) will succeed for lower PUD range and
> kvm_pud_addr_end() will return 'end' and leave the upper mappings
> stranded.
There is something I don't understand. The usual loop would be something
like (boilerplate code taken from the current KVM code base):
<quote>
static void stage2_flush_puds(struct kvm *kvm, pgd_t *pgd,
phys_addr_t addr, phys_addr_t end)
{
pud_t *pud;
phys_addr_t next;
pud = pud_offset(pgd, addr);
do {
next = kvm_pud_addr_end(addr, end);
if (!pud_none(*pud)) {
[...]
}
} while (pud++, addr = next, addr != end);
}
static void stage2_flush_memslot(struct kvm *kvm,
struct kvm_memory_slot *memslot)
{
phys_addr_t addr = memslot->base_gfn << PAGE_SHIFT;
phys_addr_t end = addr + PAGE_SIZE * memslot->npages;
phys_addr_t next;
pgd_t *pgd;
pgd = kvm->arch.pgd + pgd_index(addr);
do {
next = kvm_pgd_addr_end(addr, end);
stage2_flush_puds(kvm, pgd, addr, next);
} while (pgd++, addr = next, addr != end);
}
</quote>
If your memslot is across two pgd/pud, then kvm_pgd_addr_end will give
you the address of the next range you're interested in, and it will be
picked up at the next iteration.
/me puzzled.
M.
--
Jazz is not dead. It just smells funny.
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