From: Michael Kelley <mhkli...@outlook.com> Current code allocates the hv_vp_assist_page array with size num_possible_cpus(). This code assumes cpu_possible_mask is dense, which is not true in the general case per [1]. If cpu_possible_mask is sparse, the array might be indexed by a value beyond the size of the array.
However, the configurations that Hyper-V provides to guest VMs on x86 hardware, in combination with how x86 code assigns Linux CPU numbers, *does* always produce a dense cpu_possible_mask. So the dense assumption is not currently causing failures. But for robustness against future changes in how cpu_possible_mask is populated, update the code to no longer assume dense. The correct approach is to allocate the array with size "nr_cpu_ids". While this leaves unused array entries corresponding to holes in cpu_possible_mask, the holes are assumed to be minimal and hence the amount of memory wasted by unused entries is minimal. [1] https://lore.kernel.org/lkml/sn6pr02mb4157210cc36b2593f8572e5ed4...@sn6pr02mb4157.namprd02.prod.outlook.com/ Signed-off-by: Michael Kelley <mhkli...@outlook.com> --- arch/x86/hyperv/hv_init.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c index 95eada2994e1..2cec4dfec165 100644 --- a/arch/x86/hyperv/hv_init.c +++ b/arch/x86/hyperv/hv_init.c @@ -473,7 +473,7 @@ void __init hyperv_init(void) if (hv_isolation_type_tdx()) hv_vp_assist_page = NULL; else - hv_vp_assist_page = kcalloc(num_possible_cpus(), + hv_vp_assist_page = kcalloc(nr_cpu_ids, sizeof(*hv_vp_assist_page), GFP_KERNEL); if (!hv_vp_assist_page) { -- 2.25.1
