On Wed, Sep 2, 2026 at 11:02 AM Michael Kelley <[email protected]> wrote: > > hv_apicid_to_vp_index() currently uses the per-cpu hypercall input > and output pages. This function is called when running in VTL2 and > when running in an SEV-SNP CoCo VM with no paravisor. In the former > case, the output page is allocated, but in the latter case it is > not, so the hypervisor stores the output VP index in memory that has > not been allocated by the guest. > > Fix this by using the input page for both input and output. The > hypercall has very small input and output, so sharing the same > page for both is straightforward. An alternative fix is to > allocate the per-cpu output page when running in an SEV-SNP CoCo > guest, but this uses significantly more memory, particularly > with larger vCPUs counts. > > Fixes: 86c48271e0d6 ("x86/hyperv: Fix APIC ID and VP index confusion in > hv_snp_boot_ap()") > Signed-off-by: Michael Kelley <[email protected]> > --- > I'm not aware that this bug is causing any real problems because > SEV-SNP CoCo VMs on Hyper-V are rarely, if ever, used without a > paravisor. But it was on my list of little clean-ups to do, and > a recent Sashiko analysis [1] flagged the issue. So the best thing > to do is just fix it. Reviewed-by: Tianyu Lan <[email protected]>
> > [1] > https://lore.kernel.org/linux-hyperv/[email protected]/ > > Changes in v2: > * Make the new code a bit cleaner by dropping the unnecessary cast > to u32 * > > arch/x86/hyperv/hv_init.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c > index d5edc8530964..2a71c70d7e27 100644 > --- a/arch/x86/hyperv/hv_init.c > +++ b/arch/x86/hyperv/hv_init.c > @@ -731,7 +731,8 @@ int hv_apicid_to_vp_index(u32 apic_id) > input->partition_id = HV_PARTITION_ID_SELF; > input->apic_ids[0] = apic_id; > > - output = *this_cpu_ptr(hyperv_pcpu_output_arg); > + /* Treat input as having 2 APIC IDs so output is 64-bit aligned */ > + output = (void *)input + struct_size(input, apic_ids, 2); > > control = HV_HYPERCALL_REP_COMP_1 | HVCALL_GET_VP_INDEX_FROM_APIC_ID; > status = hv_do_hypercall(control, input, output); > -- > 2.25.1 > > -- Thanks Tianyu Lan
