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vmm: raise the (v)CPU limit on kvm/x86_64

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Raise the max number of supported (v)CPUs on kvm x86_64 hosts
to 8192 (the max allowed value of CONFIG_NR_CPUS in the Linux kernel).

Other platfroms keep their existing CPU limits pending further
development and testing.

The change has been tested on Intel and AMD hosts.

Signed-off-by: Barret Rhoden <brho@google.com>
Signed-off-by: Neel Natu <neelnatu@google.com>
Signed-off-by: Ofir Weisse <oweisse@google.com>
Signed-off-by: Peter Oskolkov <posk@google.com>
This commit is contained in:
Peter Oskolkov
2025-09-05 20:36:25 +00:00
committed by Bo Chen
parent 57bc78da4f
commit 05d222f0eb
6 changed files with 97 additions and 45 deletions
Download Patch File Download Diff File Expand all files Collapse all files
vmm/src/config.rs
+25 -5
View File
@@ -27,6 +27,11 @@ use crate::vm_config::*;
const MAX_NUM_PCI_SEGMENTS: u16 = 96;
const MAX_IOMMU_ADDRESS_WIDTH_BITS: u8 = 64;
#[cfg(all(feature = "kvm", target_arch = "x86_64"))]
const MAX_SUPPORTED_CPUS: u32 = 8192;
#[cfg(not(all(feature = "kvm", target_arch = "x86_64")))]
const MAX_SUPPORTED_CPUS: u32 = 255;
/// Errors associated with VM configuration parameters.
#[derive(Debug, Error)]
pub enum Error {
@@ -182,6 +187,9 @@ pub enum ValidationError {
/// Max is less than boot
#[error("Max CPUs lower than boot CPUs")]
CpusMaxLowerThanBoot,
/// Too many CPUs.
#[error("Too many CPUs: specified {0} but {MAX_SUPPORTED_CPUS} is the limit")]
TooManyCpus(u32 /* specified CPUs */),
/// Missing file value for debug-console
#[cfg(target_arch = "x86_64")]
#[error("Path missing when using file mode for debug console")]
@@ -586,11 +594,11 @@ impl CpusConfig {
.add("features");
parser.parse(cpus).map_err(Error::ParseCpus)?;
let boot_vcpus: u8 = parser
let boot_vcpus: u32 = parser
.convert("boot")
.map_err(Error::ParseCpus)?
.unwrap_or(DEFAULT_VCPUS);
let max_vcpus: u8 = parser
let max_vcpus: u32 = parser
.convert("max")
.map_err(Error::ParseCpus)?
.unwrap_or(boot_vcpus);
@@ -605,7 +613,7 @@ impl CpusConfig {
.map_err(Error::ParseCpus)?
.unwrap_or(DEFAULT_MAX_PHYS_BITS);
let affinity = parser
.convert::<Tuple<u8, Vec<usize>>>("affinity")
.convert::<Tuple<u32, Vec<usize>>>("affinity")
.map_err(Error::ParseCpus)?
.map(|v| {
v.0.iter()
@@ -2147,7 +2155,7 @@ impl NumaConfig {
let cpus = parser
.convert::<IntegerList>("cpus")
.map_err(Error::ParseNuma)?
.map(|v| v.0.iter().map(|e| *e as u8).collect());
.map(|v| v.0.iter().map(|e| *e as u32).collect());
let distances = parser
.convert::<Tuple<u64, u64>>("distances")
.map_err(Error::ParseNuma)?
@@ -2523,6 +2531,15 @@ impl VmConfig {
return Err(ValidationError::CpusMaxLowerThanBoot);
}
if self.cpus.max_vcpus > MAX_SUPPORTED_CPUS {
// Note: historically, Cloud Hypervisor did not support more than 255(254 on x64)
// vCPUs: self.cpus.max_vcpus was of type u8, so 255 was the maximum;
// on x86_64, the legacy mptable/apic was limited to 254 CPUs.
//
// Now the limit is lifted on x86_64 targets. Other targests/archs: TBD.
return Err(ValidationError::TooManyCpus(self.cpus.max_vcpus));
}
if let Some(rate_limit_groups) = &self.rate_limit_groups {
for rate_limit_group in rate_limit_groups {
rate_limit_group.validate(self)?;
@@ -2614,7 +2631,10 @@ impl VmConfig {
return Err(ValidationError::CpuTopologyDiesPerPackage);
}
let total = t.threads_per_core * t.cores_per_die * t.dies_per_package * t.packages;
let total: u32 = (t.threads_per_core as u32)
* (t.cores_per_die as u32)
* (t.dies_per_package as u32)
* (t.packages as u32);
if total != self.cpus.max_vcpus {
return Err(ValidationError::CpuTopologyCount);
}