linux-kernel - [PATCH v2] soc: qcom: cmd-db: Map shared memory as WC, not WB

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Message-ID: <20240718-cmd_db_uncached-v2-1-f6cf53164c90@quicinc.com>
Date: Thu, 18 Jul 2024 11:33:23 +0530
From: Maulik Shah <quic_mkshah@...cinc.com>
To: Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio
	<konrad.dybcio@...aro.org>
CC: <caleb.connolly@...aro.org>, <stephan@...hold.net>, <swboyd@...omium.org>,
        <dianders@...omium.org>, <robdclark@...il.com>, <nikita@...n.ru>,
        <quic_eberman@...cinc.com>, <quic_pkondeti@...cinc.com>,
        <quic_lsrao@...cinc.com>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Volodymyr Babchuk
	<Volodymyr_Babchuk@...m.com>,
        <stable@...r.kernel.org>,
        Volodymyr Babchuk
	<volodymyr_babchuk@...m.com>,
        Maulik Shah <quic_mkshah@...cinc.com>
Subject: [PATCH v2] soc: qcom: cmd-db: Map shared memory as WC, not WB

From: Volodymyr Babchuk <Volodymyr_Babchuk@...m.com>

Linux does not write into cmd-db region. This region of memory is write
protected by XPU. XPU may sometime falsely detect clean cache eviction
as "write" into the write protected region leading to secure interrupt
which causes an endless loop somewhere in Trust Zone.

The only reason it is working right now is because Qualcomm Hypervisor
maps the same region as Non-Cacheable memory in Stage 2 translation
tables. The issue manifests if we want to use another hypervisor (like
Xen or KVM), which does not know anything about those specific mappings.

Changing the mapping of cmd-db memory from MEMREMAP_WB to MEMREMAP_WT/WC
removes dependency on correct mappings in Stage 2 tables. This patch
fixes the issue by updating the mapping to MEMREMAP_WC.

I tested this on SA8155P with Xen.

Fixes: 312416d9171a ("drivers: qcom: add command DB driver")
Cc: stable@...r.kernel.org # 5.4+
Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@...m.com>
Tested-by: Nikita Travkin <nikita@...n.ru> # sc7180 WoA in EL2
Signed-off-by: Maulik Shah <quic_mkshah@...cinc.com>
---
Changes in v2:
 - Use MEMREMAP_WC instead of MEMREMAP_WT
 - Update commit message from comments in v1
 - Add Fixes tag and Cc to stable
 - Link to v1: https://lore.kernel.org/lkml/20240327200917.2576034-1-volodymyr_babchuk@epam.com
---
 drivers/soc/qcom/cmd-db.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/soc/qcom/cmd-db.c b/drivers/soc/qcom/cmd-db.c
index d84572662017..ae66c2623d25 100644
--- a/drivers/soc/qcom/cmd-db.c
+++ b/drivers/soc/qcom/cmd-db.c
@@ -349,7 +349,7 @@ static int cmd_db_dev_probe(struct platform_device *pdev)
 		return -EINVAL;
 	}
 
-	cmd_db_header = memremap(rmem->base, rmem->size, MEMREMAP_WB);
+	cmd_db_header = memremap(rmem->base, rmem->size, MEMREMAP_WC);
 	if (!cmd_db_header) {
 		ret = -ENOMEM;
 		cmd_db_header = NULL;

---
base-commit: 797012914d2d031430268fe512af0ccd7d8e46ef
change-id: 20240718-cmd_db_uncached-e896da5c5296

Best regards,
-- 
Maulik Shah <quic_mkshah@...cinc.com>