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.
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
