Hi Zenghui
On 04/09/2019 09:05 AM, Zenghui Yu wrote:
On 2019/4/9 2:40, Suzuki K Poulose wrote:
Hi Zenhui,
On 04/08/2019 04:11 PM, Zenghui Yu wrote:
Hi Suzuki,
Thanks for the reply.
...
Hi Suzuki,
Why not making use of fault_supports_stage2_huge_mapping()? Let it do
some checks for us.
fault_supports_stage2_huge_mapping() was intended to do a *two-step*
check to tell us that can we create stage2 huge block mappings, and
this
check is both for hugetlbfs and THP. With commit a80868f398554842b14,
we pass PAGE_SIZE as "map_size" for normal size pages (which turned
out
to be almost meaningless), and unfortunately the THP check no longer
works.
Thats correct.
So we want to rework *THP* check process. Your patch fixes the first
checking-step, but the second is still missed, am I wrong?
It fixes the step explicitly for the THP by making sure that the GPA
and
the HVA are aligned to the map size.
Yes, I understand how your patch had fixed the issue. But what I'm
really concerned about here is the *second* checking-step in
fault_supports_stage2_huge_mapping().
We have to check if we are mapping a non-block aligned or non-block
sized memslot, if so, we can not create block mappings for the beginning
and end of this memslot. This is what the second part of
fault_supports_stage2_huge_mapping() had done.
I haven't seen this checking-step in your patch, did I miss something?
I see.
I don't think this calls for a VM_BUG_ON(). It is simply a case where
the GPA is not aligned to HVA, but for normal VMA that could be made
THP.
We had this VM_BUG_ON(), which would have never hit because we would
have set force_pte if they were not aligned.
Yes, I agree.
+ /* Skip memslots with unaligned IPA and user address */
+ if ((gfn & mask) != (pfn & mask))
+ return false;
if (pfn & mask) {
*ipap &= PMD_MASK;
kvm_release_pfn_clean(pfn);
---8>---
Rework fault_supports_stage2_huge_mapping(), let it check THP again.
Signed-off-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
---
virt/kvm/arm/mmu.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
index 27c9583..5e1b258 100644
--- a/virt/kvm/arm/mmu.c
+++ b/virt/kvm/arm/mmu.c
@@ -1632,6 +1632,15 @@ static bool
fault_supports_stage2_huge_mapping(struct kvm_memory_slot *memslot,
uaddr_end = uaddr_start + size;
/*
+ * If the memslot is _not_ backed by hugetlbfs, then check if it
+ * can be backed by transparent hugepages.
+ *
+ * Currently only PMD_SIZE THPs are supported, revisit it later.
+ */
+ if (map_size == PAGE_SIZE)
+ map_size = PMD_SIZE;
+
This looks hackish. What is we support PUD_SIZE huge page in the future
?
Yes, this might make the code a little difficult to understand. But by
doing so, we follow the same logic before commit a80868f398554842b14,
that said, we do the two-step checking for normal size pages in
fault_supports_stage2_huge_mapping(), to decide if we can create THP
mappings for these pages.
As for PUD_SIZE THPs, to be honest, I have no idea now :(
How about the following diff ?
diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
index 97b5417..98e5cec 100644
--- a/virt/kvm/arm/mmu.c
+++ b/virt/kvm/arm/mmu.c
@@ -1791,7 +1791,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu,
phys_addr_t fault_ipa,
* currently supported. This code will need to be
* updated to support other THP sizes.
*/
- if (transparent_hugepage_adjust(&pfn, &fault_ipa))
+ if (fault_supports_stage2_huge_mappings(memslot, hva,
PMD_SIZE) &&
+ transparent_hugepage_adjust(&pfn, &fault_ipa))
vma_pagesize = PMD_SIZE;
}
I think this is good enough for the issue.
(One minor concern: With this change, it seems that we no longer need
"force_pte" and can just use "logging_active" instead. But this is not
much related to what we're fixing.)
I would still leave the force_pte there to avoid checking for a THP case
in a situation where we forced to PTE level mapping on a hugepage backed
VMA. It would serve to avoid another check.
Cheers
Suzuki
thanks.
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