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mshv: use VP register page for RIP/RAX writes in run_vcpu #1366

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mshv: use VP register page for RIP/RAX writes in run_vcpu #1366

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2 changes: 2 additions & 0 deletions src/hyperlight_host/src/hypervisor/virtual_machine/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -200,6 +200,8 @@ pub enum RunVcpuError {
GetDr6(HypervisorError),
#[error("Increment RIP failed: {0}")]
IncrementRip(HypervisorError),
#[error("VP register page not available")]
NoVpRegisterPage,
#[error("Parse GPA access info failed")]
ParseGpaAccessInfo,
#[error("Unknown error: {0}")]
Expand Down
59 changes: 36 additions & 23 deletions src/hyperlight_host/src/hypervisor/virtual_machine/mshv/x86_64.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -26,17 +26,16 @@ use mshv_bindings::LapicState;
#[cfg(gdb)]
use mshv_bindings::{DebugRegisters, hv_message_type_HVMSG_X64_EXCEPTION_INTERCEPT};
use mshv_bindings::{
FloatingPointUnit, SpecialRegisters, StandardRegisters, XSave, hv_message_type,
hv_message_type_HVMSG_GPA_INTERCEPT, hv_message_type_HVMSG_UNMAPPED_GPA,
FloatingPointUnit, HV_X64_REGISTER_CLASS_IP, SpecialRegisters, StandardRegisters, XSave,
hv_message_type, hv_message_type_HVMSG_GPA_INTERCEPT, hv_message_type_HVMSG_UNMAPPED_GPA,
hv_message_type_HVMSG_X64_HALT, hv_message_type_HVMSG_X64_IO_PORT_INTERCEPT,
hv_partition_property_code_HV_PARTITION_PROPERTY_SYNTHETIC_PROC_FEATURES,
hv_partition_synthetic_processor_features, hv_register_assoc,
hv_register_name_HV_X64_REGISTER_RIP, hv_register_value, mshv_create_partition_v2,
mshv_user_mem_region,
hv_partition_synthetic_processor_features, mshv_create_partition_v2, mshv_user_mem_region,
};
#[cfg(feature = "hw-interrupts")]
use mshv_bindings::{
hv_interrupt_type_HV_X64_INTERRUPT_TYPE_FIXED, hv_register_name_HV_X64_REGISTER_RAX,
HV_X64_REGISTER_CLASS_GENERAL, hv_interrupt_type_HV_X64_INTERRUPT_TYPE_FIXED,
hv_register_assoc, hv_register_value,
};
#[cfg(feature = "hw-interrupts")]
use mshv_ioctls::InterruptRequest;
Expand Down Expand Up @@ -219,16 +218,21 @@ impl VirtualMachine for MshvVm {
let instruction_length = io_message.header.instruction_length() as u64;
let is_write = io_message.header.intercept_access_type != 0;

// mshv, unlike kvm, does not automatically increment RIP
self.vcpu_fd
.set_reg(&[hv_register_assoc {
name: hv_register_name_HV_X64_REGISTER_RIP,
value: hv_register_value {
reg64: rip + instruction_length,
},
..Default::default()
}])
.map_err(|e| RunVcpuError::IncrementRip(e.into()))?;
// mshv, unlike kvm, does not automatically increment RIP.
{
let page = self
.vcpu_fd
.get_vp_reg_page()
.ok_or(RunVcpuError::NoVpRegisterPage)?;
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@syntactically syntactically Apr 20, 2026

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It looks like a lot of the code in mshv-ioctls uses VcpuFd::is_valid_vp_reg_page to check that the hypervisor has set some validity state saying that the vp reg page access works---do we need to do that as well?

// SAFETY: The register page is a valid mmap'd page
// from create_vcpu and is always populated after a
// vcpu run returns an intercept message.
unsafe {
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@simongdavies simongdavies Apr 14, 2026

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Its a pity RegisterPage doesn't have safe accessors for all the data, might be worth an upstream PR?

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@syntactically syntactically Apr 20, 2026

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It looks like upstream code uses mshv_bindings::set_gp_regs_field_ptr, e.g. here---so perhaps that at least is worth using

(*page.0).__bindgen_anon_1.__bindgen_anon_1.rip =
rip + instruction_length;
(*page.0).dirty |= 1 << HV_X64_REGISTER_CLASS_IP;
}
}

// VmAction::Halt always means "I'm done", regardless
// of whether a timer is active.
Expand All @@ -253,13 +257,22 @@ impl VirtualMachine for MshvVm {
} else if let Some(val) =
super::super::x86_64::hw_interrupts::handle_io_in(port_number)
{
self.vcpu_fd
.set_reg(&[hv_register_assoc {
name: hv_register_name_HV_X64_REGISTER_RAX,
value: hv_register_value { reg64: val },
..Default::default()
}])
.map_err(|e| RunVcpuError::Unknown(e.into()))?;
let page = self
.vcpu_fd
.get_vp_reg_page()
.ok_or(RunVcpuError::NoVpRegisterPage)?;
// SAFETY: The register page is a valid mmap'd page
// from create_vcpu and is always populated after a
// vcpu run returns an intercept message.
unsafe {
(*page.0)
.__bindgen_anon_1
.__bindgen_anon_1
.__bindgen_anon_1
.__bindgen_anon_1
.rax = val;
(*page.0).dirty |= 1 << HV_X64_REGISTER_CLASS_GENERAL;
}
continue;
}
}
Expand Down
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