Coverity: kvm_hv_flush_tlb(): Uninitialized variables

Hello!

This is an experimental semi-automated report about issues detected by Coverity from a scan of next-20221201 as part of the linux-next scan project:
https://scan.coverity.com/projects/linux-next-weekly-scan

You're getting this email because you were associated with the identified lines of code (noted below) that were touched by commits:

Fri Nov 18 12:59:05 2022 -0500

    260970862c88 ("KVM: x86: hyper-v: Handle HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST{,EX} calls gently")

Coverity reported the following:

*** CID 1527764: Uninitialized variables (UNINIT) arch/x86/kvm/hyperv.c:2024 in kvm_hv_flush_tlb()

2018     		 * Hyper-V TLFS doesn't explicitly forbid non-empty sparse vCPU
2019     		 * banks (and, thus, non-zero 'var_cnt') for the 'all vCPUs'
2020     		 * case (HV_GENERIC_SET_ALL).  Always adjust data_offset and
2021     		 * consumed_xmm_halves to make sure TLB flush entries are read
2022     		 * from the correct offset.
2023     		 */
vvv     CID 1527764:  Uninitialized variables  (UNINIT)
vvv     Using uninitialized value "data_offset".
2024     		data_offset += hc->var_cnt * sizeof(sparse_banks[0]);
2025     		consumed_xmm_halves += hc->var_cnt;
2026     	}

2027
2028 if (hc->code == HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE ||
2029 hc->code == HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX ||

If this is a false positive, please let us know so we can mark it as such, or teach the Coverity rules to be smarter. If not, please make sure fixes get into linux-next. :) For patches fixing this, please include these lines (but double-check the "Fixes" first):

Addresses-Coverity-ID: 1527764 ("Uninitialized variables")

Thanks for your attention!

Coverity-bot

Looks half legit) 'data_offset' can only be uninitialized here in 'hc->fast' case but this also means that the only user of 'data_offset' (kvm_hv_get_tlb_flush_entries()) below will not use it. So yes, we do increment an uninitialized variable but we won't use the result. I think we're better off fixing this, even if there's no real issue. I'll send a patch, hopefully tomorrow.

Thanks!

Vitaly