From 999ad14259a0d45cb3b616e2e95a7c8b622a7ecd Mon Sep 17 00:00:00 2001 From: Michael Kelley Date: Tue, 18 Mar 2025 14:49:19 -0700 Subject: x86/hyperv: Add comments about hv_vpset and var size hypercall input args Current code varies in how the size of the variable size input header for hypercalls is calculated when the input contains struct hv_vpset. Surprisingly, this variation is correct, as different hypercalls make different choices for what portion of struct hv_vpset is treated as part of the variable size input header. The Hyper-V TLFS is silent on these details, but the behavior has been confirmed with Hyper-V developers. To avoid future confusion about these differences, add comments to struct hv_vpset, and to hypercall call sites with input that contains a struct hv_vpset. The comments describe the overall situation and the calculation that should be used at each particular call site. No functional change as only comments are updated. Signed-off-by: Michael Kelley Link: https://lore.kernel.org/r/20250318214919.958953-1-mhklinux@outlook.com Signed-off-by: Wei Liu Message-ID: <20250318214919.958953-1-mhklinux@outlook.com> --- include/hyperv/hvgdk_mini.h | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) (limited to 'include/hyperv') diff --git a/include/hyperv/hvgdk_mini.h b/include/hyperv/hvgdk_mini.h index 735329859f21..abf0bd76e370 100644 --- a/include/hyperv/hvgdk_mini.h +++ b/include/hyperv/hvgdk_mini.h @@ -205,7 +205,14 @@ union hv_reference_tsc_msr { /* The number of vCPUs in one sparse bank */ #define HV_VCPUS_PER_SPARSE_BANK (64) -/* Some of Hyper-V structs do not use hv_vpset where linux uses them */ +/* + * Some of Hyper-V structs do not use hv_vpset where linux uses them. + * + * struct hv_vpset is usually used as part of hypercall input. The portion + * that counts as "fixed size input header" vs. "variable size input header" + * varies per hypercall. See comments at relevant hypercall call sites as to + * how the "valid_bank_mask" field should be accounted. + */ struct hv_vpset { /* HV_VP_SET */ u64 format; u64 valid_bank_mask; -- cgit v1.2.3