Add a XEN infix, to properly distinguish it from the CPUID feature flag
(leaf 6 EAX bit 2).
Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
Question is whether we still need opt_arat (and the command line option),
or whether we could go directly from the CPUID bit (overriding it to on
for older AMD [and Hygon?] CPUs). Or whether to have opt_arat affect the
(host) CPU policy directly.
--- a/xen/arch/x86/acpi/cpu_idle.c
+++ b/xen/arch/x86/acpi/cpu_idle.c
@@ -109,7 +109,7 @@ void (*__read_mostly lapic_timer_on)(voi
bool lapic_timer_init(void)
{
- if ( boot_cpu_has(X86_FEATURE_ARAT) )
+ if ( boot_cpu_has(X86_FEATURE_XEN_ARAT) )
{
lapic_timer_off = lapic_timer_nop;
lapic_timer_on = lapic_timer_nop;
@@ -1463,7 +1463,7 @@ static void amd_cpuidle_init(struct acpi
if ( !vendor_override )
{
- if ( !boot_cpu_has(X86_FEATURE_ARAT) )
+ if ( !boot_cpu_has(X86_FEATURE_XEN_ARAT) )
hpet_broadcast_init();
if ( !lapic_timer_init() )
--- a/xen/arch/x86/cpu/amd.c
+++ b/xen/arch/x86/cpu/amd.c
@@ -1355,7 +1355,7 @@ static void cf_check init_amd(struct cpu
* running in deep C states.
*/
if ( opt_arat && c->x86 > 0x11 )
- __set_bit(X86_FEATURE_ARAT, c->x86_capability);
+ __set_bit(X86_FEATURE_XEN_ARAT, c->x86_capability);
/*
* Prior to Family 0x14, perf counters are not reset during warm reboot.
--- a/xen/arch/x86/cpu/hygon.c
+++ b/xen/arch/x86/cpu/hygon.c
@@ -76,7 +76,7 @@ static void cf_check init_hygon(struct c
/* Hygon processors have APIC timer running in deep C states. */
if (opt_arat)
- __set_bit(X86_FEATURE_ARAT, c->x86_capability);
+ __set_bit(X86_FEATURE_XEN_ARAT, c->x86_capability);
if (cpu_has(c, X86_FEATURE_EFRO)) {
rdmsrl(MSR_K8_HWCR, value);
--- a/xen/arch/x86/cpu/intel.c
+++ b/xen/arch/x86/cpu/intel.c
@@ -668,7 +668,7 @@ static void cf_check init_intel(struct c
if ( opt_arat &&
( c->cpuid_level >= 0x00000006 ) &&
( cpuid_eax(0x00000006) & (1u<<2) ) )
- __set_bit(X86_FEATURE_ARAT, c->x86_capability);
+ __set_bit(X86_FEATURE_XEN_ARAT, c->x86_capability);
if ((opt_cpu_info && !(c->apicid & (c->x86_num_siblings - 1))) ||
c == &boot_cpu_data )
--- a/xen/arch/x86/cpu/mwait-idle.c
+++ b/xen/arch/x86/cpu/mwait-idle.c
@@ -1633,7 +1633,7 @@ static int __init mwait_idle_probe(void)
icpu = id->driver_data;
cpuidle_state_table = icpu->state_table;
- if (boot_cpu_has(X86_FEATURE_ARAT))
+ if (boot_cpu_has(X86_FEATURE_XEN_ARAT))
lapic_timer_reliable_states = LAPIC_TIMER_ALWAYS_RELIABLE;
pr_debug(PREFIX "v" MWAIT_IDLE_VERSION " model %#x\n",
@@ -1792,7 +1792,7 @@ int __init mwait_idle_init(struct notifi
return -ENODEV;
err = mwait_idle_probe();
- if (!err && !boot_cpu_has(X86_FEATURE_ARAT)) {
+ if (!err && !boot_cpu_has(X86_FEATURE_XEN_ARAT)) {
hpet_broadcast_init();
if (xen_cpuidle < 0 && !hpet_broadcast_is_available())
err = -ENODEV;
--- a/xen/arch/x86/include/asm/cpufeatures.h
+++ b/xen/arch/x86/include/asm/cpufeatures.h
@@ -13,7 +13,7 @@
/* Synthetic features */
XEN_CPUFEATURE(CONSTANT_TSC, X86_SYNTH( 0)) /* TSC ticks at a constant rate */
XEN_CPUFEATURE(NONSTOP_TSC, X86_SYNTH( 1)) /* TSC does not stop in C states */
-XEN_CPUFEATURE(ARAT, X86_SYNTH( 2)) /* Always running APIC timer */
+XEN_CPUFEATURE(XEN_ARAT, X86_SYNTH( 2)) /* Xen may utilize always running APIC timer */
XEN_CPUFEATURE(ARCH_PERFMON, X86_SYNTH( 3)) /* Intel Architectural PerfMon */
XEN_CPUFEATURE(TSC_RELIABLE, X86_SYNTH( 4)) /* TSC is known to be reliable */
XEN_CPUFEATURE(XTOPOLOGY, X86_SYNTH( 5)) /* cpu topology enum extensions */
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -2642,7 +2642,7 @@ static int _disable_pit_irq(bool init)
* XXX dom0 may rely on RTC interrupt delivery, so only enable
* hpet_broadcast if FSB mode available or if force_hpet_broadcast.
*/
- if ( cpuidle_using_deep_cstate() && !boot_cpu_has(X86_FEATURE_ARAT) )
+ if ( cpuidle_using_deep_cstate() && !boot_cpu_has(X86_FEATURE_XEN_ARAT) )
{
init ? hpet_broadcast_init() : hpet_broadcast_resume();
if ( !hpet_broadcast_is_available() )On 18/11/2025 3:07 pm, Jan Beulich wrote: > Add a XEN infix, to properly distinguish it from the CPUID feature flag > (leaf 6 EAX bit 2). > > Signed-off-by: Jan Beulich <jbeulich@suse.com> > --- > Question is whether we still need opt_arat (and the command line option), > or whether we could go directly from the CPUID bit (overriding it to on > for older AMD [and Hygon?] CPUs). Or whether to have opt_arat affect the > (host) CPU policy directly. I have no particular love for opt_arat. I added it when there was no way to force a system to fall back to an older timer. As long as we've got some way of configuring the exact timer to, I'm not fussed about keeping the top level boolean. ~Andrew
On 18.11.2025 17:38, Andrew Cooper wrote: > On 18/11/2025 3:07 pm, Jan Beulich wrote: >> Add a XEN infix, to properly distinguish it from the CPUID feature flag >> (leaf 6 EAX bit 2). >> >> Signed-off-by: Jan Beulich <jbeulich@suse.com> >> --- >> Question is whether we still need opt_arat (and the command line option), >> or whether we could go directly from the CPUID bit (overriding it to on >> for older AMD [and Hygon?] CPUs). Or whether to have opt_arat affect the >> (host) CPU policy directly. > > I have no particular love for opt_arat. I added it when there was no > way to force a system to fall back to an older timer. > > As long as we've got some way of configuring the exact timer to, I'm not > fussed about keeping the top level boolean. But the question is what the replacement would look like. Is it okay to override bits to true in the host policy? (It may be as long as we don't expose this in the guest policies, but at some point we may want or even need to.) Would the command line option also go away (in favor of integrating with cpuid=, which would require extra logic as long as we don't put leaf 6 bits in public/arch-x86/cpufeatureset.h)? IOW for the patch at hand I wouldn't mean to make adjustments. The remark was more towards further, future adjustments. Jan
© 2016 - 2026 Red Hat, Inc.