Re: [PATCH v9 6/7] iommu/arm-smmu-v3: Add arm_smmu_invs based arm_smmu_domain_inv_range()

On Tue, Jan 27, 2026 at 01:08:37PM -0400, Jason Gunthorpe wrote:

On Tue, Jan 27, 2026 at 08:38:31AM -0800, Nicolin Chen wrote:

quoted

Hi Pranjal,

Sorry, I missed this!

On Fri, Jan 23, 2026 at 09:48:37AM +0000, Pranjal Shrivastava wrote:

quoted

On Fri, Dec 19, 2025 at 12:11:28PM -0800, Nicolin Chen wrote:

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+	/*
+	 * Avoid locking unless ATS is being used. No ATC invalidation can be
+	 * going on after a domain is detached.
+	 */
+	if (invs->has_ats) {
+		read_lock(&invs->rwlock);

Shouldn't these be read_lock_irqsave for all rwlock variants here? 
Invalidations might happen in IRQ context as well..

quoted

+		__arm_smmu_domain_inv_range(invs, iova, size, granule, leaf);
+		read_unlock(&invs->rwlock);

It was kept from the older versions where we had a trylock. Jason
had an insight about this, mainly for less latency on invalidation
threads.

Yet, now we have a plain locking. TBH, I can't find a good reason
justifying this. And it does look a bit unsafe to me. So, I think
I will just change to the _irqsave version. (Jason?)

My understanding has been that this invalidation can run from an IRQ
context - we permit the use of the DMA API from an interrupt handler?

I though that for rwsem the read side does not require the _irqsave,
even if it is in an irq context, unless the write side runs from an
IRQ. 

Hmm, is "rwsem" a typo? Because it's rwlock_t, which is spinlock :-/

Here the write side always runs from a process context.

So the write side will block the IRQ which ensures we don't spin
during read in an IRQ.

And, does write_lock_irqsave() disable global IRQ or local IRQ only?

Documentation/locking/locktypes.rst mentions "local_irq_disable()"..

Thanks
Nicolin