[PATCH 2/3] sparc64: use the fault address for si_addr on window fixup faults

[Stian Halseth]

do_fault_siginfo() prefers an address decoded from the instruction at
regs->tpc whenever one could be probed, falling back to the fault time
address only when it could not.

That premise does not hold for a fault taken during a register window
spill or fill.  There the instruction at regs->tpc is the one being
resumed, not the access that faulted, so compute_effective_address()
fabricates an address out of unrelated register contents.  In one
capture it decoded a branch and reported the value it found in %g5 as
si_addr.

Use the fault time address for FAULT_CODE_WINFIXUP.  It may only have
page granularity, but it is the address that actually faulted.

Fixes: 70ffc6ebaead ("sparc64: Fix top-level fault handling bugs.")
Link: https://github.com/sparclinux/issues/issues/87
Signed-off-by: Stian Halseth <stian@xxxxxx>
---
 arch/sparc/mm/fault_64.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/sparc/mm/fault_64.c b/arch/sparc/mm/fault_64.c
index e326caf708c6..c37b24f757f4 100644
--- a/arch/sparc/mm/fault_64.c
+++ b/arch/sparc/mm/fault_64.c
@@ -165,6 +165,15 @@ static void do_fault_siginfo(int code, int sig, struct pt_regs *regs,
 
 	if (fault_code & FAULT_CODE_ITLB) {
 		addr = regs->tpc;
+	} else if (fault_code & FAULT_CODE_WINFIXUP) {
+		/* The fault came from a register window spill or fill, so
+		 * the instruction at regs->tpc is the one being resumed,
+		 * not the access that faulted.  Decoding it would fabricate
+		 * an address out of unrelated register contents; the fault
+		 * time provided address is the real one, even if it only
+		 * has page granularity.
+		 */
+		addr = fault_addr;
 	} else {
 		/* If we were able to probe the faulting instruction, use it
 		 * to compute a precise fault address.  Otherwise use the fault
-- 
2.43.0