linux-kernel - [PATCH 4.19 008/131] arm64: Fake the IminLine size on systems affected by Neoverse-N1 #1542419

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Date:   Tue, 28 Apr 2020 20:23:40 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 008/131] arm64: Fake the IminLine size on systems affected by Neoverse-N1 #1542419

From: James Morse <james.morse@....com>

[ Upstream commit ee9d90be9ddace01b7fb126567e4b539fbe1f82f ]

Systems affected by Neoverse-N1 #1542419 support DIC so do not need to
perform icache maintenance once new instructions are cleaned to the PoU.
For the errata workaround, the kernel hides DIC from user-space, so that
the unnecessary cache maintenance can be trapped by firmware.

To reduce the number of traps, produce a fake IminLine value based on
PAGE_SIZE.

Signed-off-by: James Morse <james.morse@....com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: James Morse <james.morse@....com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/arm64/include/asm/cache.h | 3 ++-
 arch/arm64/kernel/traps.c      | 8 +++++++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/cache.h b/arch/arm64/include/asm/cache.h
index 5ee5bca8c24b1..baa684782358c 100644
--- a/arch/arm64/include/asm/cache.h
+++ b/arch/arm64/include/asm/cache.h
@@ -22,6 +22,7 @@
 #define CTR_L1IP_MASK		3
 #define CTR_DMINLINE_SHIFT	16
 #define CTR_IMINLINE_SHIFT	0
+#define CTR_IMINLINE_MASK	0xf
 #define CTR_ERG_SHIFT		20
 #define CTR_CWG_SHIFT		24
 #define CTR_CWG_MASK		15
@@ -29,7 +30,7 @@
 #define CTR_DIC_SHIFT		29
 
 #define CTR_CACHE_MINLINE_MASK	\
-	(0xf << CTR_DMINLINE_SHIFT | 0xf << CTR_IMINLINE_SHIFT)
+	(0xf << CTR_DMINLINE_SHIFT | CTR_IMINLINE_MASK << CTR_IMINLINE_SHIFT)
 
 #define CTR_L1IP(ctr)		(((ctr) >> CTR_L1IP_SHIFT) & CTR_L1IP_MASK)
 
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 253b7f84a5a0d..965595fe68045 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -481,9 +481,15 @@ static void ctr_read_handler(unsigned int esr, struct pt_regs *regs)
 	int rt = (esr & ESR_ELx_SYS64_ISS_RT_MASK) >> ESR_ELx_SYS64_ISS_RT_SHIFT;
 	unsigned long val = arm64_ftr_reg_user_value(&arm64_ftr_reg_ctrel0);
 
-	if (cpus_have_const_cap(ARM64_WORKAROUND_1542419))
+	if (cpus_have_const_cap(ARM64_WORKAROUND_1542419)) {
+		/* Hide DIC so that we can trap the unnecessary maintenance...*/
 		val &= ~BIT(CTR_DIC_SHIFT);
 
+		/* ... and fake IminLine to reduce the number of traps. */
+		val &= ~CTR_IMINLINE_MASK;
+		val |= (PAGE_SHIFT - 2) & CTR_IMINLINE_MASK;
+	}
+
 	pt_regs_write_reg(regs, rt, val);
 
 	arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
-- 
2.20.1