From b5969494c8d8a2384c0636707a538efad15d8660 Mon Sep 17 00:00:00 2001 From: "Ahmed S. Darwish" Date: Mon, 24 Mar 2025 14:32:56 +0100 Subject: [PATCH] x86/cpu: Remove CPUID leaf 0x2 parsing loop Leaf 0x2 output includes a "query count" byte where it was supposed to specify the number of repeated CPUID leaf 0x2 subleaf 0 queries needed to extract all of the CPU's cache and TLB descriptors. Per current Intel manuals, all CPUs supporting this leaf "will always" return an iteration count of 1. Remove the leaf 0x2 query loop and just query the hardware once. Note, as previously done in: aec28d852ed2 ("x86/cpuid: Standardize on u32 in ") standardize on using 'u32' and 'u8' types. Suggested-by: Ingo Molnar Suggested-by: Thomas Gleixner Signed-off-by: Ahmed S. Darwish Signed-off-by: Ingo Molnar Cc: H. Peter Anvin Cc: Linus Torvalds Link: https://lore.kernel.org/r/20250324133324.23458-2-darwi@linutronix.de --- arch/x86/kernel/cpu/intel.c | 30 +++++++++++++++--------------- 1 file changed, 15 insertions(+), 15 deletions(-) diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c index 4cbb2e69bea19..0570d4d860067 100644 --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -6,6 +6,7 @@ #include #include #include +#include #ifdef CONFIG_X86_64 #include @@ -777,28 +778,27 @@ static void intel_tlb_lookup(const unsigned char desc) static void intel_detect_tlb(struct cpuinfo_x86 *c) { - int i, j, n; - unsigned int regs[4]; - unsigned char *desc = (unsigned char *)regs; + u32 regs[4]; + u8 *desc = (u8 *)regs; if (c->cpuid_level < 2) return; - /* Number of times to iterate */ - n = cpuid_eax(2) & 0xFF; + cpuid(2, ®s[0], ®s[1], ®s[2], ®s[3]); - for (i = 0 ; i < n ; i++) { - cpuid(2, ®s[0], ®s[1], ®s[2], ®s[3]); - - /* If bit 31 is set, this is an unknown format */ - for (j = 0 ; j < 4 ; j++) - if (regs[j] & (1 << 31)) - regs[j] = 0; + /* Intel CPUs must report an iteration count of 1 */ + if (desc[0] != 0x01) + return; - /* Byte 0 is level count, not a descriptor */ - for (j = 1 ; j < 16 ; j++) - intel_tlb_lookup(desc[j]); + /* If a register's bit 31 is set, it is an unknown format */ + for (int i = 0; i < 4; i++) { + if (regs[i] & (1 << 31)) + regs[i] = 0; } + + /* Skip the first byte as it is not a descriptor */ + for (int i = 1; i < 16; i++) + intel_tlb_lookup(desc[i]); } static const struct cpu_dev intel_cpu_dev = { -- 2.47.2