The rmtfs_mem region is a weird one, downstream allocates it
dynamically, and supports a "qcom,guard-memory" property which when set
will reserve 4k above and below the rmtfs memory.
A common from qcom 4.9 kernel msm_sharedmem driver:
/*
* If guard_memory is set, then the shared memory region
* will be guarded by SZ_4K at the start and at the end.
* This is needed to overcome the XPU limitation on few
* MSM HW, so as to make this memory not contiguous with
* other allocations that may possibly happen from other
* clients in the system.
*/
When the kernel tries to touch memory that is too close the
rmtfs region it may cause an XPU violation. Such is the case on the
OnePlus 6 where random crashes would occur usually after boot.
Reserve 4k above and below the rmtfs_mem to avoid hitting these XPU
Violations.
This doesn't entirely solve the random crashes on the OnePlus 6/6T but
it does seem to prevent the ones which happen shortly after modem
bringup.
Signed-off-by: Caleb Connolly <caleb@xxxxxxxxxxxxx>
---
arch/arm64/boot/dts/qcom/sdm845-oneplus-common.dtsi | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/arch/arm64/boot/dts/qcom/sdm845-oneplus-common.dtsi b/arch/arm64/boot/dts/qcom/sdm845-oneplus-common.dtsi
index 8f3f5c687b4a..96c370b90550 100644
--- a/arch/arm64/boot/dts/qcom/sdm845-oneplus-common.dtsi
+++ b/arch/arm64/boot/dts/qcom/sdm845-oneplus-common.dtsi
@@ -46,6 +46,14 @@ vol-up {
};
reserved-memory {
+ /* The rmtfs_mem needs to be guarded due to "XPU limitations"
+ * it is otherwise possible for an allocation adjacent to the
+ * rmtfs_mem region to trigger an XPU violation, causing a crash.
+ */
+ rmtfs_lower_guard: memory@f5b00000 {
+ no-map;
+ reg = <0 0xf5b00000 0 0x1000>;
+ };
/*
* The rmtfs memory region in downstream is 'dynamically allocated'
* but given the same address every time. Hard code it as this address is
@@ -59,6 +67,10 @@ rmtfs_mem: memory@f5b01000 {
qcom,client-id = <1>;
qcom,vmid = <15>;
};
+ rmtfs_upper_guard: memory@f5d01000 {
+ no-map;
+ reg = <0 0xf5d01000 0 0x2000>;
+ };
/*
* It seems like reserving the old rmtfs_mem region is also needed to prevent
--
2.30.2
