[PATCH v2 15/22] alpha: select HAVE_GUP_FAST

The lockless GUP fast path needs the architecture to distinguish PTEs
with no struct page behind them and to keep page table pages alive while
a walker holds no lock.  Alpha now has ARCH_HAS_PTE_SPECIAL, and it has
selected MMU_GATHER_RCU_TABLE_FREE for a long time, so both requirements
are met.

PTEs are a single 64-bit word on Alpha, so the lockless reads that the
generic walker performs cannot tear, and no arch-specific
gup_fast_permitted() or ptep_get_lockless() is needed.

Assisted-by: Claude:claude-opus-5
Signed-off-by: Matt Turner <mattst88@gmail.com>
Tested-by: Magnus Lindholm <linmag7@gmail.com>
Reviewed-by: Magnus Lindholm <linmag7@gmail.com>
---
 arch/alpha/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
index 4bd5e913baaf..1ba262812212 100644
--- a/arch/alpha/Kconfig
+++ b/arch/alpha/Kconfig

@@ -28,6 +28,7 @@ config ALPHA
 	select HAVE_ARCH_COMPILER_H
 	select HAVE_ASM_MODVERSIONS
 	select HAVE_DEBUG_KMEMLEAK
+	select HAVE_GUP_FAST
 	select HAVE_PAGE_SIZE_8KB
 	select HAVE_PCSPKR_PLATFORM
 	select HAVE_PERF_EVENTS

-- 
2.54.0