diff mbox series

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

Message ID 20241003035333.49261-6-mhklinux@outlook.com (mailing list archive)
State Accepted
Commit c86ab60b92d1f3471a56c8bd0856ca78e705f0f0
Delegated to: Netdev Maintainers
Headers show
Series hyper-v: Don't assume cpu_possible_mask is dense | expand

Checks

Context Check Description
netdev/series_format success Posting correctly formatted
netdev/tree_selection success Guessed tree name to be net-next
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 9 this patch: 9
netdev/build_tools success No tools touched, skip
netdev/cc_maintainers success CCed 9 of 9 maintainers
netdev/build_clang success Errors and warnings before: 9 this patch: 9
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 8 this patch: 8
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 8 lines checked
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0
netdev/contest success net-next-2024-10-04--18-00 (tests: 773)

Commit Message

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

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)