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| author | Michael Kelley <mhklinux@outlook.com> | 2024-10-03 06:53:31 +0300 |
|---|---|---|
| committer | Wei Liu <wei.liu@kernel.org> | 2025-01-10 03:54:21 +0300 |
| commit | 4f6b64f3d3d96fb3796614362c64a4b73ddf3f7a (patch) | |
| tree | 34e63b38ab226b98675f04c5dbed3267e1cc3f20 | |
| parent | 16b18fdf6bc7292ae0edbf33d2d693af3240e49d (diff) | |
| download | linux-4f6b64f3d3d96fb3796614362c64a4b73ddf3f7a.tar.xz | |
iommu/hyper-v: Don't assume cpu_possible_mask is dense
Current code gets the APIC IDs for CPUs numbered 255 and lower.
This code assumes cpu_possible_mask is dense, which is not true in
the general case per [1]. If cpu_possible_mask contains holes,
num_possible_cpus() is less than nr_cpu_ids, so some CPUs might get
skipped. Furthermore, getting the APIC ID of a CPU that isn't in
cpu_possible_mask is invalid.
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 determine the range to scan based on
nr_cpu_ids, and skip any CPUs that are not in the cpu_possible_mask.
[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/20241003035333.49261-4-mhklinux@outlook.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <20241003035333.49261-4-mhklinux@outlook.com>
| -rw-r--r-- | drivers/iommu/hyperv-iommu.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/drivers/iommu/hyperv-iommu.c b/drivers/iommu/hyperv-iommu.c index 8a5c17b97310..2a86aa5d54c6 100644 --- a/drivers/iommu/hyperv-iommu.c +++ b/drivers/iommu/hyperv-iommu.c @@ -164,8 +164,8 @@ static int __init hyperv_prepare_irq_remapping(void) * max cpu affinity for IOAPIC irqs. Scan cpu 0-255 and set cpu * into ioapic_max_cpumask if its APIC ID is less than 256. */ - for (i = min_t(unsigned int, num_possible_cpus() - 1, 255); i >= 0; i--) - if (cpu_physical_id(i) < 256) + for (i = min_t(unsigned int, nr_cpu_ids - 1, 255); i >= 0; i--) + if (cpu_possible(i) && cpu_physical_id(i) < 256) cpumask_set_cpu(i, &ioapic_max_cpumask); return 0; |