[PATCH 6/6] alpha: invalidate the local context in flush_icache_user_page()

[Magnus Lindholm <linmag7@gmail.com>]

flush_icache_user_page() has the same caller-CPU omission that the
previous patch fixed in flush_tlb_mm():

	if (mm == current->active_mm) {
		__load_new_mm_context(mm);
		...
	}

	smp_call_function(ipi_flush_icache_page, mm, 1);

When the target mm is not the calling CPU's active_mm nothing happens
locally, and smp_call_function() handles only the other CPUs, so this CPU
may later reuse the old ASN together with the translations it still holds.

This matters here in particular because the function exists for operating
on another process's mappings: the comment above it describes setting
breakpoints through ptrace, and access_remote_vm() reaches it through
copy_to_user_page(). The calling CPU is therefore often running something
other than the target mm.

As in flush_tlb_mm(), the UP implementation in asm/cacheflush.h already
has the missing case:

	if (current->active_mm == mm)
		__load_new_mm_context(mm);
	else
		mm->context[smp_processor_id()] = 0;

Signed-off-by: Magnus Lindholm <linmag7@gmail.com>
---
 arch/alpha/kernel/smp.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/alpha/kernel/smp.c b/arch/alpha/kernel/smp.c
index f501a91001cc..13b86f7224de 100644
--- a/arch/alpha/kernel/smp.c
+++ b/arch/alpha/kernel/smp.c
@@ -780,6 +780,13 @@ flush_icache_user_page(struct vm_area_struct *vma, struct page *page,
 			preempt_enable();
 			return;
 		}
+	} else {
+		/*
+		 * As in flush_tlb_mm(): smp_call_function() does not call
+		 * back into this CPU, and this function is used precisely
+		 * when operating on another process's mappings.
+		 */
+		flush_tlb_other(mm);
 	}
 
 	smp_call_function(ipi_flush_icache_page, mm, 1);
-- 
2.53.0