Ritesh Harjani (IBM) [off-list ref] writes:

Kevin Brodsky [off-list ref] writes:

quoted

Upcoming changes to the lazy_mmu API will cause
arch_flush_lazy_mmu_mode() to be called when leaving a nested
lazy_mmu section.

Move the relevant logic from arch_leave_lazy_mmu_mode() to
arch_flush_lazy_mmu_mode() and have the former call the latter.

Note: the additional this_cpu_ptr() on the
arch_leave_lazy_mmu_mode() path will be removed in a subsequent
patch.

Signed-off-by: Kevin Brodsky <redacted>
---
 .../powerpc/include/asm/book3s/64/tlbflush-hash.h | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h b/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
index 146287d9580f..7704dbe8e88d 100644
--- a/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
+++ b/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h

@@ -41,6 +41,16 @@ static inline void arch_enter_lazy_mmu_mode(void)
 	batch->active = 1;
 }
 
+static inline void arch_flush_lazy_mmu_mode(void)
+{
+	struct ppc64_tlb_batch *batch;
+
+	batch = this_cpu_ptr(&ppc64_tlb_batch);
+
+	if (batch->index)
+		__flush_tlb_pending(batch);
+}
+

This looks a bit scary since arch_flush_lazy_mmu_mode() is getting
called from several of the places in later patches(). 

Although I think arch_flush_lazy_mmu_mode() will only always be called
in nested lazy mmu case right?

Do you think we can add a VM_BUG_ON(radix_enabled()); in above to make
sure the above never gets called in radix_enabled() case. 

I am still going over the patch series, but while reviewing this I
wanted to take your opinion.

Ohh wait.. There is no way of knowing the return value from
arch_enter_lazy_mmu_mode().. I think you might need a similar check to
return from arch_flush_lazy_mmu_mode() too, if radix_enabled() is true.

Now that I have gone through this series, it seems plaussible that since
lazy mmu mode supports nesting, arch_flush_lazy_mmu_mode() can get
called while the lazy mmu is active due to nesting.. 

That means we should add the radix_enabled() check as I was talking in
above i.e. 

@@ -38,6 +38,9 @@ static inline void arch_flush_lazy_mmu_mode(void)
 {
        struct ppc64_tlb_batch *batch;

+       if (radix_enabled())
+               return;
+
        batch = this_cpu_ptr(&ppc64_tlb_batch);

        if (batch->index)

Correct? Although otherwise also I don't think it should be a problem
because batch->index is only valid during hash, but I still think we can
add above check so that we don't have to call this_cpu_ptr() to check
for batch->index whenever flush is being called.

-ritesh