[PATCH v2 7/7] 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(): 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 uniprocessor implementation in
asm/cacheflush.h already has the missing case.

No imb() is needed, here or in ipi_flush_icache_page(). Alpha's
user-space I-cache flush works by allocating a new ASN rather than by
invalidating the I-cache: the entries stay, but they are tagged with the
old ASN and can no longer match. An imb() is only required when the ASN
space wraps and numbers are reused, and __get_new_mm_context() already
does one in that case.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Magnus Lindholm <linmag7@gmail.com>
---
 arch/alpha/kernel/smp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/alpha/kernel/smp.c b/arch/alpha/kernel/smp.c
index 988e397b0b8a..e21bc3920bec 100644
--- a/arch/alpha/kernel/smp.c
+++ b/arch/alpha/kernel/smp.c
@@ -758,6 +758,9 @@ flush_icache_user_page(struct vm_area_struct *vma, struct page *page,
 			preempt_enable();
 			return;
 		}
+	} else {
+		/* smp_call_function() does not call back into this CPU.  */
+		flush_tlb_other(mm);
 	}
 
 	smp_call_function(ipi_flush_icache_page, mm, 1);
-- 
2.53.0