From: Michael Kelley Date: Thu, 3 Oct 2024 03:53:29 +0000 (-0700) Subject: x86/hyperv: Don't assume cpu_possible_mask is dense X-Git-Tag: v6.14-rc1~95^2~10 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=a7ae41cd808557c1d4e21c4295578fffcba0eb34;p=thirdparty%2Flinux.git x86/hyperv: Don't assume cpu_possible_mask is dense 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/SN6PR02MB4157210CC36B2593F8572E5ED4692@SN6PR02MB4157.namprd02.prod.outlook.com/ Signed-off-by: Michael Kelley Acked-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20241003035333.49261-2-mhklinux@outlook.com Signed-off-by: Wei Liu Message-ID: <20241003035333.49261-2-mhklinux@outlook.com> --- diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c index ba469d6b82506..f82d1aefaa8a9 100644 --- a/arch/x86/hyperv/hv_init.c +++ b/arch/x86/hyperv/hv_init.c @@ -472,7 +472,7 @@ 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) {