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[PULL 08/36] target/arm: Disable clean_data_tbi for system mode

From: Peter Maydell
Subject: [PULL 08/36] target/arm: Disable clean_data_tbi for system mode
Date: Thu, 12 Mar 2020 16:44:31 +0000

From: Richard Henderson <address@hidden>

We must include the tag in the FAR_ELx register when raising
an addressing exception.  Which means that we should not clear
out the tag during translation.

We cannot at present comply with this for user mode, so we
retain the clean_data_tbi function for the moment, though it
no longer does what it says on the tin for system mode.  This
function is to be replaced with MTE, so don't worry about the
slight misnaming.

Buglink: https://bugs.launchpad.net/qemu/+bug/1867072
Signed-off-by: Richard Henderson <address@hidden>
Message-id: address@hidden
Reviewed-by: Peter Maydell <address@hidden>
Signed-off-by: Peter Maydell <address@hidden>
 target/arm/translate-a64.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
index fefe8af7f52..8fffb52203d 100644
--- a/target/arm/translate-a64.c
+++ b/target/arm/translate-a64.c
@@ -228,7 +228,18 @@ static void gen_a64_set_pc(DisasContext *s, TCGv_i64 src)
 static TCGv_i64 clean_data_tbi(DisasContext *s, TCGv_i64 addr)
     TCGv_i64 clean = new_tmp_a64(s);
+    /*
+     * In order to get the correct value in the FAR_ELx register,
+     * we must present the memory subsystem with the "dirty" address
+     * including the TBI.  In system mode we can make this work via
+     * the TLB, dropping the TBI during translation.  But for user-only
+     * mode we don't have that option, and must remove the top byte now.
+     */
     gen_top_byte_ignore(s, clean, addr, s->tbid);
+    tcg_gen_mov_i64(clean, addr);
     return clean;

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