On Wed, Jan 08, 2025 at 12:37:17PM -0800, Roman Kisel wrote:
>
>
> On 1/8/2025 11:17 AM, Stanislav Kinsburskii wrote:
> > On Tue, Jan 07, 2025 at 03:11:15PM -0800, Roman Kisel wrote:
>
> [...]
>
> > >
> > > Avoiding using the output hypercall page leads to something like[1]
> > > and it looks quite complicated although that's the bare bones, lots
> > > of notes.
> > >
> >
> > How is this related to the original discussion?
>
> I was looking for ways to eliminate what I perceived as the source of
> friction in the discussion -- allocating the hypercall output page.
>
No, output page allocation is the current solution and it is fine.
The source of friction is allocation of this page under config option in
runtime.
Thanks,
Stas
> > My concern was about the piece allocating of the output page guarded by
> > the VTL config option.>> Thanks,
> > Stas
> >
> > > [1]
> > >
> > > /*
> > > * Fast extended hypercall with 20 bytes of input and 16 bytes of
> > > * output for getting a VP register.
> > > *
> > > * NOTES:
> > > * 1. The function is __init only atm, so the XMM context isn't
> > > * used by the user mode.
> > > * 2. X86_64 only.
> > > * 3. Fast extended hypercalls may use XMM0..XMM6, and XMM is
> > > * architerctural on X86_64 yet the support should be enabled
> > > * in the CR's. Here, need RDX, R8 and XMM0 for input and RDX,
> > > * R8 for output
> > > * 4. No provisions for TDX and SEV-SNP for the sake of simplicity
> > > * (the hypervisor cannot see the guest registers in the
> > > * confidential VM), would need to fallback.
> > > * 5. The robust implementation would need to check if fast extended
> > > * hypercalls are available by checking the synthehtic CPUID leaves.
> > > * A separate leaf indicates fast output support.
> > > * It _almost_ certainly has to be, unless somehow disabled, hard
> > > * to see why that would be needed.
> > > */
> > > struct hv_u128 {
> > > u64 low_part;
> > > u64 high_part;
> > > } __packed;
> > >
> > > static __init u64 hv_vp_get_register_xfast(u32 reg_name,
> > > struct hv_u128 *value)
> > > {
> > > u64 control = HV_HYPERCALL_REP_COMP_1 | HVCALL_GET_VP_REGISTERS |
> > > HV_HYPERCALL_FAST_BIT;
> > > unsigned long flags;
> > > u64 hv_status;
> > >
> > > union {
> > > struct hv_get_vp_registers_input input;
> > > struct {
> > > u64 lo;
> > > u64 hi;
> > > } __packed as_u128;
> > > } hv_input;
> > > register u64 rdx asm("rdx");
> > > register u64 r8 asm("r8");
> > > register u64 r12 asm("r12");
> > >
> > > local_irq_save(flags);
> > >
> > > hv_input.as_u128.lo = hv_input.as_u128.hi = 0;
> > > hv_input.input.header.partitionid = HV_PARTITION_ID_SELF;
> > > hv_input.input.header.vpindex = HV_VP_INDEX_SELF;
> > > hv_input.input.header.inputvtl = 0;
> > >
> > > rdx = hv_input.as_u128.lo;
> > > r8 = hv_input.as_u128.hi;
> > > r12 = reg_name;
> > >
> > > __asm__ __volatile__(
> > > "subq $16, %%rsp\n"
> > > "movups %%xmm0, 16(%%rsp)\n"
> > > "movd %%r12, %%xmm0\n"
> > > CALL_NOSPEC
> > > "movups 16(%%rsp), %%xmm0\n"
> > > "addq $16, %%rsp\n"
> > > : "=a" (hv_status), ASM_CALL_CONSTRAINT,
> > > "+c" (control), "+r" (rdx), "+r" (r8)
> > > : THUNK_TARGET(hv_hypercall_pg), "r"(r12)
> > > : "cc", "memory", "r9", "r10", "r11");
> > >
> > > if (hv_result_success(hv_status)) {
> > > value->low_part = rdx;
> > > value->high_part = r8;
> > > }
> > >
> > > local_irq_restore(flags);
> > > return hv_status;
> > > }
> > >
> > > #if IS_ENABLED(CONFIG_HYPERV_VTL_MODE)
> > > u8 __init get_vtl(void)
> > > {
> > > struct hv_u128 reg_value;
> > > u64 ret = hv_vp_get_register_xfast(HV_REGISTER_VSM_VP_STATUS,
> > > ®_value);
> > >
> > > if (hv_result_success(ret)) {
> > > ret = reg_value.low_part & HV_VTL_MASK;
> > > } else {
> > > pr_err("Failed to get VTL(error: %lld) exiting...\n", ret);
> > > BUG();
> > > }
> > >
> > > return ret;
> > > }
> > > #endif
> > >
> > > >
> > > > Thanks,
> > > > Stas
> > >
> > > --
> > > Thank you,
> > > Roman
> > >
>
> --
> Thank you,
> Roman
>
