The following commit has been merged into the x86/urgent branch of tip: Commit-ID: c064b536a8f9ab7c8e204da8f5a22f7420d0b56c Gitweb: https://git.kernel.org/tip/c064b536a8f9ab7c8e204da8f5a22f7420d0b56c Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx> AuthorDate: Wed, 10 Apr 2024 21:45:28 +02:00 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitterDate: Fri, 12 Apr 2024 12:05:54 +02:00 x86/cpu/amd: Make the NODEID_MSR union actually work A system with NODEID_MSR was reported to crash during early boot without any output. The reason is that the union which is used for accessing the bitfields in the MSR is written wrongly and the resulting executable code accesses the wrong part of the MSR data. As a consequence a later division by that value results in 0 and that result is used for another division as divisor, which obviously does not work well. The magic world of C, unions and bitfields: union { u64 bita : 3, bitb : 3; u64 all; } x; x.all = foo(); a = x.bita; b = x.bitb; results in the effective executable code of: a = b = x.bita; because bita and bitb are treated as union members and therefore both end up at bit offset 0. Wrapping the bitfield into an anonymous struct: union { struct { u64 bita : 3, bitb : 3; }; u64 all; } x; works like expected. Rework the NODEID_MSR union in exactly that way to cure the problem. Fixes: f7fb3b2dd92c ("x86/cpu: Provide an AMD/HYGON specific topology parser") Reported-by: "kernelci.org bot" <bot@xxxxxxxxxxxx> Reported-by: Laura Nao <laura.nao@xxxxxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Tested-by: Laura Nao <laura.nao@xxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20240410194311.596282919@xxxxxxxxxxxxx Closes: https://lore.kernel.org/all/20240322175210.124416-1-laura.nao@xxxxxxxxxxxxx/ --- arch/x86/kernel/cpu/topology_amd.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/cpu/topology_amd.c b/arch/x86/kernel/cpu/topology_amd.c index 79a85a4..7f999ae 100644 --- a/arch/x86/kernel/cpu/topology_amd.c +++ b/arch/x86/kernel/cpu/topology_amd.c @@ -121,13 +121,13 @@ static bool parse_8000_001e(struct topo_scan *tscan, bool has_0xb) static bool parse_fam10h_node_id(struct topo_scan *tscan) { - struct { - union { + union { + struct { u64 node_id : 3, nodes_per_pkg : 3, unused : 58; - u64 msr; }; + u64 msr; } nid; if (!boot_cpu_has(X86_FEATURE_NODEID_MSR))