linux-kernel - [PATCH v2 3/6] firmware: qcom: scm: Handle various probe ordering for qcom_scm_assign

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Message-Id: <20241209-qcom-scm-missing-barriers-and-all-sort-of-srap-v2-3-9061013c8d92@linaro.org>
Date: Mon, 09 Dec 2024 15:27:56 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Bjorn Andersson <andersson@...nel.org>, 
 Konrad Dybcio <konradybcio@...nel.org>, 
 Mukesh Ojha <quic_mojha@...cinc.com>, 
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, 
 Stephan Gerhold <stephan.gerhold@...aro.org>, 
 Bartosz Golaszewski <bartosz.golaszewski@...aro.org>, 
 Kuldeep Singh <quic_kuldsing@...cinc.com>, 
 Elliot Berman <quic_eberman@...cinc.com>, 
 Andrew Halaney <ahalaney@...hat.com>, 
 Avaneesh Kumar Dwivedi <quic_akdwived@...cinc.com>, 
 Andy Gross <andy.gross@...aro.org>
Cc: linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Subject: [PATCH v2 3/6] firmware: qcom: scm: Handle various probe ordering
 for qcom_scm_assign_mem()

The SCM driver can defer or fail probe, or just load a bit later so
callers of qcom_scm_assign_mem() should defer if the device is not ready.

This fixes theoretical NULL pointer exception, triggered via introducing
probe deferral in SCM driver with call trace:

  qcom_tzmem_alloc+0x70/0x1ac (P)
  qcom_tzmem_alloc+0x64/0x1ac (L)
  qcom_scm_assign_mem+0x78/0x194
  qcom_rmtfs_mem_probe+0x2d4/0x38c
  platform_probe+0x68/0xc8

Fixes: d82bd359972a ("firmware: scm: Add new SCM call API for switching memory ownership")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>

---

I am not sure about commit introducing it (Fixes tag) thus not Cc-ing
stable.
---
 drivers/firmware/qcom/qcom_scm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
index 5d91b8e22844608f35432f1ba9c08d477d4ff762..93212c8f20ad65ecc44804b00f4b93e3eaaf8d95 100644
--- a/drivers/firmware/qcom/qcom_scm.c
+++ b/drivers/firmware/qcom/qcom_scm.c
@@ -1075,6 +1075,9 @@ int qcom_scm_assign_mem(phys_addr_t mem_addr, size_t mem_sz,
 	int ret, i, b;
 	u64 srcvm_bits = *srcvm;
 
+	if (!qcom_scm_is_available())
+		return -EPROBE_DEFER;
+
 	src_sz = hweight64(srcvm_bits) * sizeof(*src);
 	mem_to_map_sz = sizeof(*mem_to_map);
 	dest_sz = dest_cnt * sizeof(*destvm);

-- 
2.43.0