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vmm: cpu: Disable KVM_FEATURE_ASYNC_PF_INT in CPUID

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By disabling this KVM feature, we prevent the guest from using APF
(Asynchronous Page Fault) mechanism. The kernel has recently switched to
using interrupts to notify about a page being ready, but for some
reasons, this is causing unexpected behavior with Cloud Hypervisor, as
it will make the vcpu thread spin at 100%.

While investigating the issue, it's better to disable the KVM feature to
prevent 100% CPU usage in some cases.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
This commit is contained in:
Sebastien Boeuf 2021-04-15 09:38:59 +02:00 committed by Rob Bradford
parent d4eaf746b5
commit b92fe648e9
1 changed files with 19 additions and 3 deletions
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20
vmm/src/cpu.rs
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@ -59,6 +59,10 @@ const HYPERVISOR_ECX_BIT: u8 = 31; // Hypervisor ecx bit.
#[cfg(target_arch = "x86_64")]
const MTRR_EDX_BIT: u8 = 12; // Hypervisor ecx bit.
// KVM feature bits
#[cfg(target_arch = "x86_64")]
const KVM_FEATURE_ASYNC_PF_INT_BIT: u8 = 14;
#[cfg(feature = "acpi")]
pub const CPU_MANAGER_ACPI_SIZE: usize = 0xc;
@ -685,11 +689,23 @@ impl CpuManager {
.map_err(Error::CpuidSgx)?;
}
// Set CPU physical bits
// Update some existing CPUID
for entry in cpuid.as_mut_slice().iter_mut() {
if entry.function == 0x8000_0008 {
match entry.function {
// Set CPU physical bits
0x8000_0008 => {
entry.eax = (entry.eax & 0xffff_ff00) | (phys_bits as u32 & 0xff);
}
// Disable KVM_FEATURE_ASYNC_PF_INT
// This is required until we find out why the asynchronous page
// fault is generating unexpected behavior when using interrupt
// mechanism.
// TODO: Re-enable KVM_FEATURE_ASYNC_PF_INT (#2277)
0x4000_0001 => {
entry.eax &= !(1 << KVM_FEATURE_ASYNC_PF_INT_BIT);
}
_ => {}
}
}
// Copy CPU identification string