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pvh: Initialize vCPU regs/sregs for PVH boot

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Set the initial values of the KVM vCPU registers as specified in
the PVH boot ABI:

https://xenbits.xen.org/docs/unstable/misc/pvh.html

Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
This commit is contained in:
Alejandro Jimenez 2020-02-11 23:48:09 -05:00 committed by Sebastien Boeuf
parent 24f0e42e6a
commit 840a9a97ff
3 changed files with 113 additions and 32 deletions
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32
arch/src/x86_64/gdt.rs
View File

@ -1,3 +1,5 @@
// Copyright © 2020, Oracle and/or its affiliates.
//
// Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
//
@ -24,8 +26,34 @@ fn get_base(entry: u64) -> u64 {
| (((entry) & 0x00000000FFFF0000) >> 16)
}
// Extract the segment limit from the GDT segment descriptor.
//
// In a segment descriptor, the limit field is 20 bits, so it can directly describe
// a range from 0 to 0xFFFFF (1MByte). When G flag is set (4-KByte page granularity) it
// scales the value in the limit field by a factor of 2^12 (4Kbytes), making the effective
// limit range from 0xFFF (4 KBytes) to 0xFFFF_FFFF (4 GBytes).
//
// However, the limit field in the VMCS definition is a 32 bit field, and the limit value is not
// automatically scaled using the G flag. This means that for a desired range of 4GB for a
// given segment, its limit must be specified as 0xFFFF_FFFF. Therefore the method of obtaining
// the limit from the GDT entry is not sufficient, since it only provides 20 bits when 32 bits
// are necessary. Fortunately, we can check if the G flag is set when extracting the limit since
// the full GDT entry is passed as an argument, and perform the scaling of the limit value to
// return the full 32 bit value.
//
// The scaling mentioned above is required when using PVH boot, since the guest boots in protected
// (32-bit) mode and must be able to access the entire 32-bit address space. It does not cause issues
// for the case of direct boot to 64-bit (long) mode, since in 64-bit mode the processor does not
// perform runtime limit checking on code or data segments.
fn get_limit(entry: u64) -> u32 {
((((entry) & 0x000F000000000000) >> 32) | ((entry) & 0x000000000000FFFF)) as u32
let limit: u32 =
((((entry) & 0x000F000000000000) >> 32) | ((entry) & 0x000000000000FFFF)) as u32;
// Perform manual limit scaling if G flag is set
match get_g(entry) {
0 => limit,
_ => ((limit << 12) | 0xFFF), // G flag is either 0 or 1
}
}
fn get_g(entry: u64) -> u8 {
@ -109,7 +137,7 @@ mod tests {
assert_eq!(0xB, seg.type_);
// base and limit
assert_eq!(0x100000, seg.base);
assert_eq!(0xfffff, seg.limit);
assert_eq!(0xffffffff, seg.limit);
assert_eq!(0x0, seg.unusable);
}
}

104
arch/src/x86_64/regs.rs
View File

@ -1,3 +1,5 @@
// Copyright © 2020, Oracle and/or its affiliates.
//
// Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
//
@ -8,10 +10,11 @@
use std::{mem, result};
use super::gdt::{gdt_entry, kvm_segment_from_gdt};
use super::BootProtocol;
use arch_gen::x86::msr_index;
use kvm_bindings::{kvm_fpu, kvm_msr_entry, kvm_regs, kvm_sregs, Msrs};
use kvm_ioctls::VcpuFd;
use layout::{BOOT_GDT_START, BOOT_IDT_START, PDE_START, PDPTE_START, PML4_START};
use layout::{BOOT_GDT_START, BOOT_IDT_START, PDE_START, PDPTE_START, PML4_START, PVH_INFO_START};
use vm_memory::{Address, Bytes, GuestMemory, GuestMemoryError, GuestMemoryMmap};
// MTRR constants
@ -81,16 +84,31 @@ pub fn setup_msrs(vcpu: &VcpuFd) -> Result<()> {
/// * `boot_ip` - Starting instruction pointer.
/// * `boot_sp` - Starting stack pointer.
/// * `boot_si` - Must point to zero page address per Linux ABI.
pub fn setup_regs(vcpu: &VcpuFd, boot_ip: u64, boot_sp: u64, boot_si: u64) -> Result<()> {
let regs: kvm_regs = kvm_regs {
rflags: 0x0000000000000002u64,
rip: boot_ip,
rsp: boot_sp,
rbp: boot_sp,
rsi: boot_si,
..Default::default()
pub fn setup_regs(
vcpu: &VcpuFd,
boot_ip: u64,
boot_sp: u64,
boot_si: u64,
boot_prot: BootProtocol,
) -> Result<()> {
let regs: kvm_regs = match boot_prot {
// Configure regs as required by PVH boot protocol.
BootProtocol::PvhBoot => kvm_regs {
rflags: 0x0000000000000002u64,
rbx: PVH_INFO_START.raw_value(),
rip: boot_ip,
..Default::default()
},
// Configure regs as required by Linux 64-bit boot protocol.
BootProtocol::LinuxBoot => kvm_regs {
rflags: 0x0000000000000002u64,
rip: boot_ip,
rsp: boot_sp,
rbp: boot_sp,
rsi: boot_si,
..Default::default()
},
};
vcpu.set_regs(&regs).map_err(Error::SetBaseRegisters)
}
@ -100,11 +118,14 @@ pub fn setup_regs(vcpu: &VcpuFd, boot_ip: u64, boot_sp: u64, boot_si: u64) -> Re
///
/// * `mem` - The memory that will be passed to the guest.
/// * `vcpu` - Structure for the VCPU that holds the VCPU's fd.
pub fn setup_sregs(mem: &GuestMemoryMmap, vcpu: &VcpuFd) -> Result<()> {
pub fn setup_sregs(mem: &GuestMemoryMmap, vcpu: &VcpuFd, boot_prot: BootProtocol) -> Result<()> {
let mut sregs: kvm_sregs = vcpu.get_sregs().map_err(Error::GetStatusRegisters)?;
configure_segments_and_sregs(mem, &mut sregs)?;
setup_page_tables(mem, &mut sregs)?; // TODO(dgreid) - Can this be done once per system instead?
configure_segments_and_sregs(mem, &mut sregs, boot_prot)?;
if let BootProtocol::LinuxBoot = boot_prot {
setup_page_tables(mem, &mut sregs)?; // TODO(dgreid) - Can this be done once per system instead?
}
vcpu.set_sregs(&sregs).map_err(Error::SetStatusRegisters)
}
@ -136,13 +157,31 @@ fn write_idt_value(val: u64, guest_mem: &GuestMemoryMmap) -> Result<()> {
.map_err(Error::WriteIDT)
}
fn configure_segments_and_sregs(mem: &GuestMemoryMmap, sregs: &mut kvm_sregs) -> Result<()> {
let gdt_table: [u64; BOOT_GDT_MAX as usize] = [
gdt_entry(0, 0, 0), // NULL
gdt_entry(0xa09b, 0, 0xfffff), // CODE
gdt_entry(0xc093, 0, 0xfffff), // DATA
gdt_entry(0x808b, 0, 0xfffff), // TSS
];
fn configure_segments_and_sregs(
mem: &GuestMemoryMmap,
sregs: &mut kvm_sregs,
boot_prot: BootProtocol,
) -> Result<()> {
let gdt_table: [u64; BOOT_GDT_MAX as usize] = match boot_prot {
BootProtocol::PvhBoot => {
// Configure GDT entries as specified by PVH boot protocol
[
gdt_entry(0, 0, 0), // NULL
gdt_entry(0xc09b, 0, 0xffffffff), // CODE
gdt_entry(0xc093, 0, 0xffffffff), // DATA
gdt_entry(0x008b, 0, 0x67), // TSS
]
}
BootProtocol::LinuxBoot => {
// Configure GDT entries as specified by Linux 64bit boot protocol
[
gdt_entry(0, 0, 0), // NULL
gdt_entry(0xa09b, 0, 0xfffff), // CODE
gdt_entry(0xc093, 0, 0xfffff), // DATA
gdt_entry(0x808b, 0, 0xfffff), // TSS
]
}
};
let code_seg = kvm_segment_from_gdt(gdt_table[1], 1);
let data_seg = kvm_segment_from_gdt(gdt_table[2], 2);
@ -165,9 +204,17 @@ fn configure_segments_and_sregs(mem: &GuestMemoryMmap, sregs: &mut kvm_sregs) ->
sregs.ss = data_seg;
sregs.tr = tss_seg;
/* 64-bit protected mode */
sregs.cr0 |= X86_CR0_PE;
sregs.efer |= EFER_LME | EFER_LMA;
match boot_prot {
BootProtocol::PvhBoot => {
sregs.cr0 = X86_CR0_PE;
sregs.cr4 = 0;
}
BootProtocol::LinuxBoot => {
/* 64-bit protected mode */
sregs.cr0 |= X86_CR0_PE;
sregs.efer |= EFER_LME | EFER_LMA;
}
}
Ok(())
}
@ -280,7 +327,7 @@ mod tests {
fn segments_and_sregs() {
let mut sregs: kvm_sregs = Default::default();
let gm = create_guest_mem();
configure_segments_and_sregs(&gm, &mut sregs).unwrap();
configure_segments_and_sregs(&gm, &mut sregs, BootProtocol::LinuxBoot).unwrap();
assert_eq!(0x0, read_u64(&gm, BOOT_GDT_START));
assert_eq!(
@ -298,13 +345,13 @@ mod tests {
assert_eq!(0x0, read_u64(&gm, BOOT_IDT_START));
assert_eq!(0, sregs.cs.base);
assert_eq!(0xfffff, sregs.ds.limit);
assert_eq!(0xffffffff, sregs.ds.limit);
assert_eq!(0x10, sregs.es.selector);
assert_eq!(1, sregs.fs.present);
assert_eq!(1, sregs.gs.g);
assert_eq!(0, sregs.ss.avl);
assert_eq!(0, sregs.tr.base);
assert_eq!(0xfffff, sregs.tr.limit);
assert_eq!(0xffffffff, sregs.tr.limit);
assert_eq!(0, sregs.tr.avl);
assert_eq!(X86_CR0_PE, sregs.cr0);
assert_eq!(EFER_LME | EFER_LMA, sregs.efer);
@ -398,6 +445,7 @@ mod tests {
expected_regs.rip,
expected_regs.rsp,
expected_regs.rsi,
BootProtocol::LinuxBoot,
)
.unwrap();
@ -413,10 +461,10 @@ mod tests {
let mut expected_sregs: kvm_sregs = vcpu.get_sregs().unwrap();
let gm = create_guest_mem();
configure_segments_and_sregs(&gm, &mut expected_sregs).unwrap();
configure_segments_and_sregs(&gm, &mut expected_sregs, BootProtocol::LinuxBoot).unwrap();
setup_page_tables(&gm, &mut expected_sregs).unwrap();
setup_sregs(&gm, &vcpu).unwrap();
setup_sregs(&gm, &vcpu, BootProtocol::LinuxBoot).unwrap();
let actual_sregs: kvm_sregs = vcpu.get_sregs().unwrap();
assert_eq!(expected_sregs, actual_sregs);
}

9
vmm/src/cpu.rs
View File

@ -296,11 +296,16 @@ impl Vcpu {
kernel_entry_point.entry_addr.raw_value(),
arch::x86_64::layout::BOOT_STACK_POINTER.raw_value(),
arch::x86_64::layout::ZERO_PAGE_START.raw_value(),
kernel_entry_point.protocol,
)
.map_err(Error::REGSConfiguration)?;
arch::x86_64::regs::setup_fpu(&self.fd).map_err(Error::FPUConfiguration)?;
arch::x86_64::regs::setup_sregs(&vm_memory.memory(), &self.fd)
.map_err(Error::SREGSConfiguration)?;
arch::x86_64::regs::setup_sregs(
&vm_memory.memory(),
&self.fd,
kernel_entry_point.protocol,
)
.map_err(Error::SREGSConfiguration)?;
}
arch::x86_64::interrupts::set_lint(&self.fd).map_err(Error::LocalIntConfiguration)?;
Ok(())