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

Commit Message

Michael Kelley Oct. 3, 2024, 3:53 a.m. UTC

From: Michael Kelley <[e-mail]>

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/[e-mail]/

Signed-off-by: Michael Kelley <[e-mail]>
---
 drivers/net/hyperv/netvsc_drv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Patch

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)