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From:   Leo Yan <leo.yan@linaro.org>
To:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Kees Cook <keescook@chromium.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Sami Tolvanen <samitolvanen@google.com>,
        Nicholas Piggin <npiggin@gmail.com>,
        James Morse <james.morse@arm.com>,
        Marc Zyngier <maz@kernel.org>, Joey Gouly <joey.gouly@arm.com>,
        Peter Collingbourne <pcc@google.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Stephane Eranian <eranian@google.com>,
        James Clark <james.clark@arm.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Cc:     Leo Yan <leo.yan@linaro.org>
Subject: [RFCv1 2/4] arm64: entry: Always apply workaround for contextidr_el1
Date:   Thu, 21 Oct 2021 21:45:28 +0800
Message-Id: <20211021134530.206216-3-leo.yan@linaro.org>
In-Reply-To: <20211021134530.206216-1-leo.yan@linaro.org>
References: <20211021134530.206216-1-leo.yan@linaro.org>
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After introducing static key as the switch for tracing PID into
contextidr_el1, the kernel can dynamically turn on the static key to
use PID tracing to contextidr_el1.  This means even the config
CONFIG_PID_IN_CONTEXTIDR is not selected, the kernel still can use
contextidr_el1.

When erratum 84571 is detected, the workaround should be always
applied on contextidr_el1, particularly if the static key is enabled
dynamically.

This patch would introduce minor overload by one extra instruction for
accessing system register contextidr_el1 and it only impacts platform
which erratum 84571.  So it's expected to not cause any significant
regression.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
---
 arch/arm64/kernel/entry.S | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index bc6d5a970a13..c41a4cfff527 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -356,12 +356,8 @@ alternative_else_nop_endif
 
 #ifdef CONFIG_ARM64_ERRATUM_845719
 alternative_if ARM64_WORKAROUND_845719
-#ifdef CONFIG_PID_IN_CONTEXTIDR
 	mrs	x29, contextidr_el1
 	msr	contextidr_el1, x29
-#else
-	msr contextidr_el1, xzr
-#endif
 alternative_else_nop_endif
 #endif
 3:
-- 
2.25.1