On 10/4/24 22:01, Sam Edwards wrote:
The CFE bootloader places a stub program in the first page of physical memory to hold the secondary CPUs until the boot CPU writes the release address, but does not splice a /reserved-memory node into the FDT to protect it. If Linux overwrites this program before execution reaches smp_prepare_cpus(), the secondary CPUs may become inaccessible. This is only a problem with CFE, and then only until the secondary CPUs are brought online. Ideally, there would be some hypothetical mechanism we could use to indicate that this area of memory is sensitive only during boot. But as there is none, and since it is such a small amount of memory, it is easiest to reserve it unconditionally.
If we supported CPU hotplug on those platforms (do we?) then it actually does matter that this memory remains protected, and it cannot be reclaimed. This does not invalidate the commit message and I will take it as-is, but it it is not memory that we can necessarily reclaim that easily, if we did things properly.
Therefore, add a /reserved-memory node to bcm4908.dtsi to protect the first 4KiB of physical memory. Signed-off-by: Sam Edwards <CFSworks@xxxxxxxxx> --- arch/arm64/boot/dts/broadcom/bcmbca/bcm4908.dtsi | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/arch/arm64/boot/dts/broadcom/bcmbca/bcm4908.dtsi b/arch/arm64/boot/dts/broadcom/bcmbca/bcm4908.dtsi index 8b924812322c..c51b92387fad 100644 --- a/arch/arm64/boot/dts/broadcom/bcmbca/bcm4908.dtsi +++ b/arch/arm64/boot/dts/broadcom/bcmbca/bcm4908.dtsi @@ -68,6 +68,16 @@ l2: l2-cache0 { }; };+ reserved-memory {+ #address-cells = <2>; + #size-cells = <2>; + ranges; + + cfe-stub@0 { + reg = <0x0 0x0 0x0 0x1000>; + }; + }; + axi@81000000 { compatible = "simple-bus"; #address-cells = <1>;
-- Florian
