Re: [PATCH 3/3] arm64: Unconditionally enable EPAN support

On Thu, 22 Jan 2026 10:15:56 +0000,
Will Deacon [off-list ref] wrote:

On Wed, Jan 07, 2026 at 06:07:01PM +0000, Marc Zyngier wrote:

quoted

While FEAT_PAN3 is pretty recent, having it permanently enabled costs
exactly nothing, and does help with exec-only mappings on these fancy
ARMv9.2 machines that are rumoured to exist.

I'm not sure it's _entirely_ accurate to say this one costs us "exactly
nothing":

quoted

diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index 177c691914f87..13c0fa54ea19f 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h

@@ -19,8 +19,6 @@ cpucap_is_possible(const unsigned int cap)
 			   "cap must be < ARM64_NCAPS");
 
 	switch (cap) {
-	case ARM64_HAS_EPAN:
-		return IS_ENABLED(CONFIG_ARM64_EPAN);
 	case ARM64_SVE:
 		return IS_ENABLED(CONFIG_ARM64_SVE);
 	case ARM64_SME:

as this means cpus_have_cap(EPAN) always ends up doing a test_bit(). It's
not exactly expensive, but it feels a little premature when compared to
PAN and LSE so I'll probably just take those changes for now.

Ah, fair enough. It can probably wait another few years then!

Cheers,

	M.

-- 
Without deviation from the norm, progress is not possible.