* [patch 1/2] KVM: x86: move nsec_to_cycles from x86.c to x86.h
2016-06-21 1:28 [patch 0/2] fix lapic_timer_advance_ns guest triggerable unlimited delays Marcelo Tosatti
@ 2016-06-21 1:28 ` Marcelo Tosatti
2016-06-21 1:28 ` [patch 2/2] KVM: LAPIC: cap __delay at lapic_timer_advance_ns Marcelo Tosatti
2016-06-21 7:53 ` [patch 0/2] fix lapic_timer_advance_ns guest triggerable unlimited delays Paolo Bonzini
2 siblings, 0 replies; 6+ messages in thread
From: Marcelo Tosatti @ 2016-06-21 1:28 UTC (permalink / raw)
To: kvm; +Cc: Paolo Bonzini, Radim Krcmar, Alan Jenkins, Marcelo Tosatti
[-- Attachment #1: move-nsecs-to-cycles --]
[-- Type: text/plain, Size: 1229 bytes --]
Move the inline function nsec_to_cycles from x86.c to x86.h, as
the next patch uses it from lapic.c.
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Index: kvm/arch/x86/kvm/x86.c
===================================================================
--- kvm.orig/arch/x86/kvm/x86.c
+++ kvm/arch/x86/kvm/x86.c
@@ -1205,12 +1205,6 @@ static atomic_t kvm_guest_has_master_clo
static DEFINE_PER_CPU(unsigned long, cpu_tsc_khz);
static unsigned long max_tsc_khz;
-static inline u64 nsec_to_cycles(struct kvm_vcpu *vcpu, u64 nsec)
-{
- return pvclock_scale_delta(nsec, vcpu->arch.virtual_tsc_mult,
- vcpu->arch.virtual_tsc_shift);
-}
-
static u32 adjust_tsc_khz(u32 khz, s32 ppm)
{
u64 v = (u64)khz * (1000000 + ppm);
Index: kvm/arch/x86/kvm/x86.h
===================================================================
--- kvm.orig/arch/x86/kvm/x86.h
+++ kvm/arch/x86/kvm/x86.h
@@ -174,4 +174,10 @@ extern unsigned int min_timer_period_us;
extern unsigned int lapic_timer_advance_ns;
extern struct static_key kvm_no_apic_vcpu;
+
+static inline u64 nsec_to_cycles(struct kvm_vcpu *vcpu, u64 nsec)
+{
+ return pvclock_scale_delta(nsec, vcpu->arch.virtual_tsc_mult,
+ vcpu->arch.virtual_tsc_shift);
+}
#endif
^ permalink raw reply [flat|nested] 6+ messages in thread* [patch 2/2] KVM: LAPIC: cap __delay at lapic_timer_advance_ns
2016-06-21 1:28 [patch 0/2] fix lapic_timer_advance_ns guest triggerable unlimited delays Marcelo Tosatti
2016-06-21 1:28 ` [patch 1/2] KVM: x86: move nsec_to_cycles from x86.c to x86.h Marcelo Tosatti
@ 2016-06-21 1:28 ` Marcelo Tosatti
2016-06-21 1:33 ` [patch 2/2 V2] " Marcelo Tosatti
2016-06-21 7:53 ` [patch 0/2] fix lapic_timer_advance_ns guest triggerable unlimited delays Paolo Bonzini
2 siblings, 1 reply; 6+ messages in thread
From: Marcelo Tosatti @ 2016-06-21 1:28 UTC (permalink / raw)
To: kvm; +Cc: Paolo Bonzini, Radim Krcmar, Alan Jenkins, Marcelo Tosatti
[-- Attachment #1: lapic-cap-wait --]
[-- Type: text/plain, Size: 1009 bytes --]
The host timer which emulates the guest LAPIC TSC deadline
timer has its expiration diminished by lapic_timer_advance_ns
nanoseconds. Therefore if, at wait_lapic_expire, a difference
larger than lapic_timer_advance_ns is encountered, delay at most
lapic_timer_advance_ns.
This fixes a problem where the guest can cause the host
to delay for large amounts of time.
Reported-by: Alan Jenkins <alan.christopher.jenkins@gmail.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Index: kvm/arch/x86/kvm/lapic.c
===================================================================
--- kvm.orig/arch/x86/kvm/lapic.c
+++ kvm/arch/x86/kvm/lapic.c
@@ -1164,7 +1164,8 @@ void wait_lapic_expire(struct kvm_vcpu *
/* __delay is delay_tsc whenever the hardware has TSC, thus always. */
if (guest_tsc < tsc_deadline)
- __delay(tsc_deadline - guest_tsc);
+ __delay(max(tsc_deadline - guest_tsc,
+ nsec_to_cycles(vcpu, lapic_timer_advance_ns)));
}
static void start_apic_timer(struct kvm_lapic *apic)
^ permalink raw reply [flat|nested] 6+ messages in thread
* [patch 2/2 V2] KVM: LAPIC: cap __delay at lapic_timer_advance_ns
2016-06-21 1:28 ` [patch 2/2] KVM: LAPIC: cap __delay at lapic_timer_advance_ns Marcelo Tosatti
@ 2016-06-21 1:33 ` Marcelo Tosatti
2016-06-21 12:13 ` Alan Jenkins
0 siblings, 1 reply; 6+ messages in thread
From: Marcelo Tosatti @ 2016-06-21 1:33 UTC (permalink / raw)
To: kvm; +Cc: Paolo Bonzini, Radim Krcmar, Alan Jenkins
The host timer which emulates the guest LAPIC TSC deadline
timer has its expiration diminished by lapic_timer_advance_ns
nanoseconds. Therefore if, at wait_lapic_expire, a difference
larger than lapic_timer_advance_ns is encountered, delay at most
lapic_timer_advance_ns.
This fixes a problem where the guest can cause the host
to delay for large amounts of time.
Reported-by: Alan Jenkins <alan.christopher.jenkins@gmail.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
---
v2: s/max/min/ !
Index: kvm/arch/x86/kvm/lapic.c
===================================================================
--- kvm.orig/arch/x86/kvm/lapic.c
+++ kvm/arch/x86/kvm/lapic.c
@@ -1164,7 +1164,8 @@ void wait_lapic_expire(struct kvm_vcpu *
/* __delay is delay_tsc whenever the hardware has TSC, thus always. */
if (guest_tsc < tsc_deadline)
- __delay(tsc_deadline - guest_tsc);
+ __delay(min(tsc_deadline - guest_tsc,
+ nsec_to_cycles(vcpu, lapic_timer_advance_ns)));
}
static void start_apic_timer(struct kvm_lapic *apic)
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [patch 2/2 V2] KVM: LAPIC: cap __delay at lapic_timer_advance_ns
2016-06-21 1:33 ` [patch 2/2 V2] " Marcelo Tosatti
@ 2016-06-21 12:13 ` Alan Jenkins
0 siblings, 0 replies; 6+ messages in thread
From: Alan Jenkins @ 2016-06-21 12:13 UTC (permalink / raw)
To: Marcelo Tosatti; +Cc: kvm, Paolo Bonzini, Radim Krcmar
On 21/06/2016, Marcelo Tosatti <mtosatti@redhat.com> wrote:
> The host timer which emulates the guest LAPIC TSC deadline
> timer has its expiration diminished by lapic_timer_advance_ns
> nanoseconds. Therefore if, at wait_lapic_expire, a difference
> larger than lapic_timer_advance_ns is encountered, delay at most
> lapic_timer_advance_ns.
>
> This fixes a problem where the guest can cause the host
> to delay for large amounts of time.
>
> Reported-by: Alan Jenkins <alan.christopher.jenkins@gmail.com>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
>
> ---
>
> v2: s/max/min/ !
>
> Index: kvm/arch/x86/kvm/lapic.c
> ===================================================================
> --- kvm.orig/arch/x86/kvm/lapic.c
> +++ kvm/arch/x86/kvm/lapic.c
> @@ -1164,7 +1164,8 @@ void wait_lapic_expire(struct kvm_vcpu *
>
> /* __delay is delay_tsc whenever the hardware has TSC, thus always. */
> if (guest_tsc < tsc_deadline)
> - __delay(tsc_deadline - guest_tsc);
> + __delay(min(tsc_deadline - guest_tsc,
> + nsec_to_cycles(vcpu, lapic_timer_advance_ns)));
> }
>
> static void start_apic_timer(struct kvm_lapic *apic)
>
Can we make sure this is sent to -stable?
Since I tested this approach (I think complete with the same max/min
correction :) before I started trying to boil the ocean, it looks good
to me.
I expect nsec_to_cycles() always rounds down. Any rounding up would be
undesirable :) - but this way, even if host sets tsc_khz=1, all that
can happen is the guest is woken 1 tick before the deadline is met. It
wouldn't be a whole millisecond early in real time either, just as
much as lapic_timer_advance_ns.
And talking of scaling, it will cut off the other potential lockup as
well where we currently fail to scale the guest delay down into host
TSC ticks.
I also suggested guests could observe early wakeup when sysadmins tune
lapic_timer_advance_ns (i.e. it was reduced after the timer was set).
But Paolo pointed out the nice way to fix that would be to make
lapic_timer_advance_ns read-only (explicit requirement to `rmmod kvm`
before you can try a different value).
Thanks for this
Alan
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [patch 0/2] fix lapic_timer_advance_ns guest triggerable unlimited delays
2016-06-21 1:28 [patch 0/2] fix lapic_timer_advance_ns guest triggerable unlimited delays Marcelo Tosatti
2016-06-21 1:28 ` [patch 1/2] KVM: x86: move nsec_to_cycles from x86.c to x86.h Marcelo Tosatti
2016-06-21 1:28 ` [patch 2/2] KVM: LAPIC: cap __delay at lapic_timer_advance_ns Marcelo Tosatti
@ 2016-06-21 7:53 ` Paolo Bonzini
2 siblings, 0 replies; 6+ messages in thread
From: Paolo Bonzini @ 2016-06-21 7:53 UTC (permalink / raw)
To: Marcelo Tosatti, kvm; +Cc: Radim Krcmar, Alan Jenkins
On 21/06/2016 03:28, Marcelo Tosatti wrote:
> The host timer which emulates the guest LAPIC TSC deadline
> timer has its expiration diminished by lapic_timer_advance_ns
> nanoseconds. Therefore if, at wait_lapic_expire, a difference
> larger than lapic_timer_advance_ns is encountered, delay at most
> lapic_timer_advance_ns.
>
> This fixes a problem where the guest can cause the host
> to delay for large amounts of time.
>
> Thanks to Alan Jenkins for reporting.
Applying to kvm/master, thanks.
Paolo
^ permalink raw reply [flat|nested] 6+ messages in thread