From cb6075bc62dc6a9cd7ab3572758685fdf78e3e20 Mon Sep 17 00:00:00 2001 From: Rik van Riel Date: Fri, 6 Jun 2025 13:10:34 -0400 Subject: [PATCH] x86/mm: Fix early boot use of INVPLGB The INVLPGB instruction has limits on how many pages it can invalidate at once. That limit is enumerated in CPUID, read by the kernel, and stored in 'invpgb_count_max'. Ranged invalidation, like invlpgb_kernel_range_flush() break up their invalidations so that they do not exceed the limit. However, early boot code currently attempts to do ranged invalidation before populating 'invlpgb_count_max'. There is a for loop which is basically: for (...; addr < end; addr += invlpgb_count_max*PAGE_SIZE) If invlpgb_kernel_range_flush is called before the kernel has read the value of invlpgb_count_max from the hardware, the normally bounded loop can become an infinite loop if invlpgb_count_max is initialized to zero. Fix that issue by initializing invlpgb_count_max to 1. This way INVPLGB at early boot time will be a little bit slower than normal (with initialized invplgb_count_max), and not an instant hang at bootup time. Fixes: b7aa05cbdc52 ("x86/mm: Add INVLPGB support code") Signed-off-by: Rik van Riel Signed-off-by: Dave Hansen Link: https://lore.kernel.org/all/20250606171112.4013261-3-riel%40surriel.com --- arch/x86/kernel/cpu/amd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index 93da466dfe2cb..b2ad8d13211ac 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -31,7 +31,7 @@ #include "cpu.h" -u16 invlpgb_count_max __ro_after_init; +u16 invlpgb_count_max __ro_after_init = 1; static inline int rdmsrq_amd_safe(unsigned msr, u64 *p) { -- 2.47.2