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KVM: PPC: Book3S HV: Make secondary threads more robust against stray IPIs

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Currently on POWER7, if we are running the guest on a core and we don't
need all the hardware threads, we do nothing to ensure that the unused
threads aren't executing in the kernel (other than checking that they
are offline).  We just assume they're napping and we don't do anything
to stop them trying to enter the kernel while the guest is running.
This means that a stray IPI can wake up the hardware thread and it will
then try to enter the kernel, but since the core is in guest context,
it will execute code from the guest in hypervisor mode once it turns the
MMU on, which tends to lead to crashes or hangs in the host.

This fixes the problem by adding two new one-byte flags in the
kvmppc_host_state structure in the PACA which are used to interlock
between the primary thread and the unused secondary threads when entering
the guest.  With these flags, the primary thread can ensure that the
unused secondaries are not already in kernel mode (i.e. handling a stray
IPI) and then indicate that they should not try to enter the kernel
if they do get woken for any reason.  Instead they will go into KVM code,
find that there is no vcpu to run, acknowledge and clear the IPI and go
back to nap mode.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Paul Mackerras 2012-02-03 00:54:17 +00:00 committed by Avi Kivity
parent f6127716c3
commit f0888f7015
6 changed files with 124 additions and 46 deletions
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8
arch/powerpc/include/asm/kvm_book3s_asm.h
View file

@ -79,6 +79,9 @@ struct kvmppc_host_state {
u8 napping;
#ifdef CONFIG_KVM_BOOK3S_64_HV
u8 hwthread_req;
u8 hwthread_state;
struct kvm_vcpu *kvm_vcpu;
struct kvmppc_vcore *kvm_vcore;
unsigned long xics_phys;
@ -122,4 +125,9 @@ struct kvmppc_book3s_shadow_vcpu {
#endif /*__ASSEMBLY__ */
/* Values for kvm_state */
#define KVM_HWTHREAD_IN_KERNEL 0
#define KVM_HWTHREAD_IN_NAP 1
#define KVM_HWTHREAD_IN_KVM 2
#endif /* __ASM_KVM_BOOK3S_ASM_H__ */

2
arch/powerpc/kernel/asm-offsets.c
View file

@ -540,6 +540,8 @@ int main(void)
HSTATE_FIELD(HSTATE_IN_GUEST, in_guest);
HSTATE_FIELD(HSTATE_RESTORE_HID5, restore_hid5);
HSTATE_FIELD(HSTATE_NAPPING, napping);
HSTATE_FIELD(HSTATE_HWTHREAD_REQ, hwthread_req);
HSTATE_FIELD(HSTATE_HWTHREAD_STATE, hwthread_state);
#ifdef CONFIG_KVM_BOOK3S_64_HV
HSTATE_FIELD(HSTATE_KVM_VCPU, kvm_vcpu);

12
arch/powerpc/kernel/exceptions-64s.S
View file

@ -63,11 +63,13 @@ BEGIN_FTR_SECTION
GET_PACA(r13)
#ifdef CONFIG_KVM_BOOK3S_64_HV
lbz r0,PACAPROCSTART(r13)
cmpwi r0,0x80
bne 1f
li r0,1
stb r0,PACAPROCSTART(r13)
li r0,KVM_HWTHREAD_IN_KERNEL
stb r0,HSTATE_HWTHREAD_STATE(r13)
/* Order setting hwthread_state vs. testing hwthread_req */
sync
lbz r0,HSTATE_HWTHREAD_REQ(r13)
cmpwi r0,0
beq 1f
b kvm_start_guest
1:
#endif

7
arch/powerpc/kernel/idle_power7.S
View file

@ -16,6 +16,7 @@
#include <asm/asm-offsets.h>
#include <asm/ppc-opcode.h>
#include <asm/hw_irq.h>
#include <asm/kvm_book3s_asm.h>
#undef DEBUG
@ -81,6 +82,12 @@ _GLOBAL(power7_idle)
std r9,_MSR(r1)
std r1,PACAR1(r13)
#ifdef CONFIG_KVM_BOOK3S_64_HV
/* Tell KVM we're napping */
li r4,KVM_HWTHREAD_IN_NAP
stb r4,HSTATE_HWTHREAD_STATE(r13)
#endif
/* Magic NAP mode enter sequence */
std r0,0(r1)
ptesync

49
arch/powerpc/kvm/book3s_hv.c
View file

@ -569,6 +569,45 @@ static void kvmppc_remove_runnable(struct kvmppc_vcore *vc,
list_del(&vcpu->arch.run_list);
}
static int kvmppc_grab_hwthread(int cpu)
{
struct paca_struct *tpaca;
long timeout = 1000;
tpaca = &paca[cpu];
/* Ensure the thread won't go into the kernel if it wakes */
tpaca->kvm_hstate.hwthread_req = 1;
/*
* If the thread is already executing in the kernel (e.g. handling
* a stray interrupt), wait for it to get back to nap mode.
* The smp_mb() is to ensure that our setting of hwthread_req
* is visible before we look at hwthread_state, so if this
* races with the code at system_reset_pSeries and the thread
* misses our setting of hwthread_req, we are sure to see its
* setting of hwthread_state, and vice versa.
*/
smp_mb();
while (tpaca->kvm_hstate.hwthread_state == KVM_HWTHREAD_IN_KERNEL) {
if (--timeout <= 0) {
pr_err("KVM: couldn't grab cpu %d\n", cpu);
return -EBUSY;
}
udelay(1);
}
return 0;
}
static void kvmppc_release_hwthread(int cpu)
{
struct paca_struct *tpaca;
tpaca = &paca[cpu];
tpaca->kvm_hstate.hwthread_req = 0;
tpaca->kvm_hstate.kvm_vcpu = NULL;
}
static void kvmppc_start_thread(struct kvm_vcpu *vcpu)
{
int cpu;
@ -588,8 +627,7 @@ static void kvmppc_start_thread(struct kvm_vcpu *vcpu)
smp_wmb();
#if defined(CONFIG_PPC_ICP_NATIVE) && defined(CONFIG_SMP)
if (vcpu->arch.ptid) {
tpaca->cpu_start = 0x80;
wmb();
kvmppc_grab_hwthread(cpu);
xics_wake_cpu(cpu);
++vc->n_woken;
}
@ -639,7 +677,7 @@ static int kvmppc_run_core(struct kvmppc_vcore *vc)
struct kvm_vcpu *vcpu, *vcpu0, *vnext;
long ret;
u64 now;
int ptid;
int ptid, i;
/* don't start if any threads have a signal pending */
list_for_each_entry(vcpu, &vc->runnable_threads, arch.run_list)
@ -686,12 +724,17 @@ static int kvmppc_run_core(struct kvmppc_vcore *vc)
vc->napping_threads = 0;
list_for_each_entry(vcpu, &vc->runnable_threads, arch.run_list)
kvmppc_start_thread(vcpu);
/* Grab any remaining hw threads so they can't go into the kernel */
for (i = ptid; i < threads_per_core; ++i)
kvmppc_grab_hwthread(vc->pcpu + i);
preempt_disable();
spin_unlock(&vc->lock);
kvm_guest_enter();
__kvmppc_vcore_entry(NULL, vcpu0);
for (i = 0; i < threads_per_core; ++i)
kvmppc_release_hwthread(vc->pcpu + i);
spin_lock(&vc->lock);
/* disable sending of IPIs on virtual external irqs */

92
arch/powerpc/kvm/book3s_hv_rmhandlers.S
View file

@ -26,6 +26,7 @@
#include <asm/hvcall.h>
#include <asm/asm-offsets.h>
#include <asm/exception-64s.h>
#include <asm/kvm_book3s_asm.h>
/*****************************************************************************
* *
@ -82,6 +83,7 @@ _GLOBAL(kvmppc_hv_entry_trampoline)
#define XICS_XIRR 4
#define XICS_QIRR 0xc
#define XICS_IPI 2 /* interrupt source # for IPIs */
/*
* We come in here when wakened from nap mode on a secondary hw thread.
@ -94,27 +96,55 @@ kvm_start_guest:
subi r1,r1,STACK_FRAME_OVERHEAD
ld r2,PACATOC(r13)
li r0,KVM_HWTHREAD_IN_KVM
stb r0,HSTATE_HWTHREAD_STATE(r13)
/* NV GPR values from power7_idle() will no longer be valid */
li r0,1
stb r0,PACA_NAPSTATELOST(r13)
/* get vcpu pointer, NULL if we have no vcpu to run */
ld r4,HSTATE_KVM_VCPU(r13)
cmpdi cr1,r4,0
/* Check the wake reason in SRR1 to see why we got here */
mfspr r3,SPRN_SRR1
rlwinm r3,r3,44-31,0x7 /* extract wake reason field */
cmpwi r3,4 /* was it an external interrupt? */
bne 27f
/*
* External interrupt - for now assume it is an IPI, since we
* should never get any other interrupts sent to offline threads.
* Only do this for secondary threads.
*/
beq cr1,25f
lwz r3,VCPU_PTID(r4)
cmpwi r3,0
beq 27f
25: ld r5,HSTATE_XICS_PHYS(r13)
li r0,0xff
li r6,XICS_QIRR
li r7,XICS_XIRR
lwzcix r8,r5,r7 /* get and ack the interrupt */
sync
clrldi. r9,r8,40 /* get interrupt source ID. */
beq 27f /* none there? */
cmpwi r9,XICS_IPI
bne 26f
stbcix r0,r5,r6 /* clear IPI */
26: stwcix r8,r5,r7 /* EOI the interrupt */
27: /* XXX should handle hypervisor maintenance interrupts etc. here */
/* if we have no vcpu to run, go back to sleep */
beq cr1,kvm_no_guest
/* were we napping due to cede? */
lbz r0,HSTATE_NAPPING(r13)
cmpwi r0,0
bne kvm_end_cede
/* get vcpu pointer */
ld r4, HSTATE_KVM_VCPU(r13)
/* We got here with an IPI; clear it */
ld r5, HSTATE_XICS_PHYS(r13)
li r0, 0xff
li r6, XICS_QIRR
li r7, XICS_XIRR
lwzcix r8, r5, r7 /* ack the interrupt */
sync
stbcix r0, r5, r6 /* clear it */
stwcix r8, r5, r7 /* EOI it */
/* NV GPR values from power7_idle() will no longer be valid */
stb r0, PACA_NAPSTATELOST(r13)
.global kvmppc_hv_entry
kvmppc_hv_entry:
@ -1445,8 +1475,8 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_206)
* Take a nap until a decrementer or external interrupt occurs,
* with PECE1 (wake on decr) and PECE0 (wake on external) set in LPCR
*/
li r0,0x80
stb r0,PACAPROCSTART(r13)
li r0,1
stb r0,HSTATE_HWTHREAD_REQ(r13)
mfspr r5,SPRN_LPCR
ori r5,r5,LPCR_PECE0 | LPCR_PECE1
mtspr SPRN_LPCR,r5
@ -1463,26 +1493,7 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_206)
kvm_end_cede:
/* Woken by external or decrementer interrupt */
ld r1, HSTATE_HOST_R1(r13)
ld r2, PACATOC(r13)
/* If we're a secondary thread and we got here by an IPI, ack it */
ld r4,HSTATE_KVM_VCPU(r13)
lwz r3,VCPU_PTID(r4)
cmpwi r3,0
beq 27f
mfspr r3,SPRN_SRR1
rlwinm r3,r3,44-31,0x7 /* extract wake reason field */
cmpwi r3,4 /* was it an external interrupt? */
bne 27f
ld r5, HSTATE_XICS_PHYS(r13)
li r0,0xff
li r6,XICS_QIRR
li r7,XICS_XIRR
lwzcix r8,r5,r7 /* ack the interrupt */
sync
stbcix r0,r5,r6 /* clear it */
stwcix r8,r5,r7 /* EOI it */
27:
/* load up FP state */
bl kvmppc_load_fp
@ -1580,12 +1591,17 @@ secondary_nap:
stwcx. r3, 0, r4
bne 51b
kvm_no_guest:
li r0, KVM_HWTHREAD_IN_NAP
stb r0, HSTATE_HWTHREAD_STATE(r13)
li r0, 0
std r0, HSTATE_KVM_VCPU(r13)
li r3, LPCR_PECE0
mfspr r4, SPRN_LPCR
rlwimi r4, r3, 0, LPCR_PECE0 | LPCR_PECE1
mtspr SPRN_LPCR, r4
isync
li r0, 0
std r0, HSTATE_SCRATCH0(r13)
ptesync
ld r0, HSTATE_SCRATCH0(r13)