From: Stanislav Kinsburskii <skinsburskii@xxxxxxxxxxxxxxxxxxx> Sent: Friday, January 3, 2025 11:20 AM
>
> On Mon, Dec 30, 2024 at 10:09:39AM -0800, Roman Kisel wrote:
> > Due to the hypercall page not being allocated in the VTL mode,
> > the code resorts to using a part of the input page.
> >
> > Allocate the hypercall output page in the VTL mode thus enabling
> > it to use it for output and share code with dom0.
> >
> > Signed-off-by: Roman Kisel <romank@xxxxxxxxxxxxxxxxxxx>
> > ---
> > drivers/hv/hv_common.c | 6 +++---
> > 1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
> > index c6ed3ba4bf61..c983cfd4d6c0 100644
> > --- a/drivers/hv/hv_common.c
> > +++ b/drivers/hv/hv_common.c
> > @@ -340,7 +340,7 @@ int __init hv_common_init(void)
> > BUG_ON(!hyperv_pcpu_input_arg);
> >
> > /* Allocate the per-CPU state for output arg for root */
> > - if (hv_root_partition) {
> > + if (hv_root_partition || IS_ENABLED(CONFIG_HYPERV_VTL_MODE)) {
>
> This check doesn't look nice.
> First of all, IS_ENABLED(CONFIG_HYPERV_VTL_MODE) doesn't mean that this
> particular kernel is being booted in VTL other that VTL0.
Actually, it does mean that. Kernels built with CONFIG_HYPERV_VTL_MODE=y
will not run as a normal guest in VTL 0. See the third paragraph of the
"help" section for HYPERV_VTL_MODE in drivers/hv/Kconfig.
Michael
>
> Second, current approach is that a VTL1+ kernel is a different build from VTL0
> kernel and thus relying on the config option looks reasonable. However,
> this is not true in general case.
>
> I'd suggest one of the following three options:
>
> 1. Always allocate per-cpu output pages. This is wasteful for the VTL0
> guest case, but it might worth it for overall simplification.
>
> 2. Don't touch this code and keep the cnage in the Underhill tree.
>
> 3. Introduce a configuration option (command line or device tree or
> both) and use it instead of the kernel config option.
>
> Thanks,
> Stas
>
> > hyperv_pcpu_output_arg = alloc_percpu(void *);
> > BUG_ON(!hyperv_pcpu_output_arg);
> > }
> > @@ -435,7 +435,7 @@ int hv_common_cpu_init(unsigned int cpu)
> > void **inputarg, **outputarg;
> > u64 msr_vp_index;
> > gfp_t flags;
> > - int pgcount = hv_root_partition ? 2 : 1;
> > + const int pgcount = (hv_root_partition ||
> IS_ENABLED(CONFIG_HYPERV_VTL_MODE)) ? 2 : 1;
> > void *mem;
> > int ret;
> >
> > @@ -453,7 +453,7 @@ int hv_common_cpu_init(unsigned int cpu)
> > if (!mem)
> > return -ENOMEM;
> >
> > - if (hv_root_partition) {
> > + if (hv_root_partition || IS_ENABLED(CONFIG_HYPERV_VTL_MODE)) {
> > outputarg = (void **)this_cpu_ptr(hyperv_pcpu_output_arg);
> > *outputarg = (char *)mem + HV_HYP_PAGE_SIZE;
> > }
> > --
> > 2.34.1
> >
