[PATCH net-next 5/5] hv_netvsc: Don't assume cpu_possible_mask is dense

mhkelley58
2024-10-03T03:54:19Z

From: Michael Kelley <mhklinux@outlook.com>

Current code allocates the pcpu_sum array with size num_possible_cpus().
This code assumes the 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
and ARM64 hardware, in combination with how architecture specific 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 and initialize the array using 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 <mhklinux@outlook.com>
---
drivers/net/hyperv/netvsc_drv.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index 153b97f8ec0d..f8e2dd6d271d 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -1557,7 +1557,7 @@ static void netvsc_get_ethtool_stats(struct net_device *dev,
data[i++] = xdp_tx;
}

- pcpu_sum = kvmalloc_array(num_possible_cpus(),
+ pcpu_sum = kvmalloc_array(nr_cpu_ids,
sizeof(struct netvsc_ethtool_pcpu_stats),
GFP_KERNEL);
if (!pcpu_sum)
--
2.25.1