diff options
| author | Michael Kelley <mhklinux@outlook.com> | 2024-10-02 20:53:30 -0700 |
|---|---|---|
| committer | Wei Liu <wei.liu@kernel.org> | 2025-01-10 00:54:21 +0000 |
| commit | 16b18fdf6bc7292ae0edbf33d2d693af3240e49d (patch) | |
| tree | 9a315096a55c4abe426aebdb45fc49304581ab07 /drivers/hv | |
| parent | a7ae41cd808557c1d4e21c4295578fffcba0eb34 (diff) | |
Drivers: hv: Don't assume cpu_possible_mask is dense
Current code allocates the hv_vp_index 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
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.
Using nr_cpu_ids also reduces initialization time, in that the loop to
initialize the array currently rescans cpu_possible_mask on each
iteration. This is n-squared in the number of CPUs, which could be
significant for large CPU counts.
[1] https://lore.kernel.org/lkml/SN6PR02MB4157210CC36B2593F8572E5ED4692@SN6PR02MB4157.namprd02.prod.outlook.com/
Signed-off-by: Michael Kelley <mhklinux@outlook.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20241003035333.49261-3-mhklinux@outlook.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <20241003035333.49261-3-mhklinux@outlook.com>
Diffstat (limited to 'drivers/hv')
| -rw-r--r-- | drivers/hv/hv_common.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c index c4fd07d9bf1a..c6ed3ba4bf61 100644 --- a/drivers/hv/hv_common.c +++ b/drivers/hv/hv_common.c @@ -345,14 +345,14 @@ int __init hv_common_init(void) BUG_ON(!hyperv_pcpu_output_arg); } - hv_vp_index = kmalloc_array(num_possible_cpus(), sizeof(*hv_vp_index), + hv_vp_index = kmalloc_array(nr_cpu_ids, sizeof(*hv_vp_index), GFP_KERNEL); if (!hv_vp_index) { hv_common_free(); return -ENOMEM; } - for (i = 0; i < num_possible_cpus(); i++) + for (i = 0; i < nr_cpu_ids; i++) hv_vp_index[i] = VP_INVAL; return 0; |