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[1/5] x86/hyperv: Don't assume cpu_possible_mask is dense

Message ID 20241003035333.49261-2-mhklinux@outlook.com (mailing list archive)
State Not Applicable
Delegated to: Netdev Maintainers
Headers show
Series hyper-v: Don't assume cpu_possible_mask is dense | expand

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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 11 of 11 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: 11 this patch: 11
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
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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 hv_vp_assist_page 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
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 allocate the array with 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>
---
 arch/x86/hyperv/hv_init.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 95eada2994e1..2cec4dfec165 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -473,7 +473,7 @@  void __init hyperv_init(void)
 	if (hv_isolation_type_tdx())
 		hv_vp_assist_page = NULL;
 	else
-		hv_vp_assist_page = kcalloc(num_possible_cpus(),
+		hv_vp_assist_page = kcalloc(nr_cpu_ids,
 					    sizeof(*hv_vp_assist_page),
 					    GFP_KERNEL);
 	if (!hv_vp_assist_page) {