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KVM: PPC: Book3S HV: Use bitmap of active threads rather than count

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Currently, the entry_exit_count field in the kvmppc_vcore struct
contains two 8-bit counts, one of the threads that have started entering
the guest, and one of the threads that have started exiting the guest.
This changes it to an entry_exit_map field which contains two bitmaps
of 8 bits each.  The advantage of doing this is that it gives us a
bitmap of which threads need to be signalled when exiting the guest.
That means that we no longer need to use the trick of setting the
HDEC to 0 to pull the other threads out of the guest, which led in
some cases to a spurious HDEC interrupt on the next guest entry.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>
This commit is contained in:
Paul Mackerras 2015-03-28 14:21:09 +11:00 committed by Alexander Graf
parent fd6d53b124
commit 7d6c40da19
5 changed files with 44 additions and 49 deletions
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15
arch/powerpc/include/asm/kvm_host.h
View File

@ -263,15 +263,15 @@ struct kvm_arch {
/*
* Struct for a virtual core.
* Note: entry_exit_count combines an entry count in the bottom 8 bits
* and an exit count in the next 8 bits. This is so that we can
* atomically increment the entry count iff the exit count is 0
* without taking the lock.
* Note: entry_exit_map combines a bitmap of threads that have entered
* in the bottom 8 bits and a bitmap of threads that have exited in the
* next 8 bits. This is so that we can atomically set the entry bit
* iff the exit map is 0 without taking a lock.
*/
struct kvmppc_vcore {
int n_runnable;
int num_threads;
int entry_exit_count;
int entry_exit_map;
int napping_threads;
int first_vcpuid;
u16 pcpu;
@ -296,8 +296,9 @@ struct kvmppc_vcore {
ulong conferring_threads;
};
#define VCORE_ENTRY_COUNT(vc) ((vc)->entry_exit_count & 0xff)
#define VCORE_EXIT_COUNT(vc) ((vc)->entry_exit_count >> 8)
#define VCORE_ENTRY_MAP(vc) ((vc)->entry_exit_map & 0xff)
#define VCORE_EXIT_MAP(vc) ((vc)->entry_exit_map >> 8)
#define VCORE_IS_EXITING(vc) (VCORE_EXIT_MAP(vc) != 0)
/* Values for vcore_state */
#define VCORE_INACTIVE 0

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

@ -562,7 +562,7 @@ int main(void)
DEFINE(VCPU_ACOP, offsetof(struct kvm_vcpu, arch.acop));
DEFINE(VCPU_WORT, offsetof(struct kvm_vcpu, arch.wort));
DEFINE(VCPU_SHADOW_SRR1, offsetof(struct kvm_vcpu, arch.shadow_srr1));
DEFINE(VCORE_ENTRY_EXIT, offsetof(struct kvmppc_vcore, entry_exit_count));
DEFINE(VCORE_ENTRY_EXIT, offsetof(struct kvmppc_vcore, entry_exit_map));
DEFINE(VCORE_IN_GUEST, offsetof(struct kvmppc_vcore, in_guest));
DEFINE(VCORE_NAPPING_THREADS, offsetof(struct kvmppc_vcore, napping_threads));
DEFINE(VCORE_KVM, offsetof(struct kvmppc_vcore, kvm));

5
arch/powerpc/kvm/book3s_hv.c
View File

@ -1952,7 +1952,7 @@ static void kvmppc_run_core(struct kvmppc_vcore *vc)
/*
* Initialize *vc.
*/
vc->entry_exit_count = 0;
vc->entry_exit_map = 0;
vc->preempt_tb = TB_NIL;
vc->in_guest = 0;
vc->napping_threads = 0;
@ -2119,8 +2119,7 @@ static int kvmppc_run_vcpu(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
* this thread straight away and have it join in.
*/
if (!signal_pending(current)) {
if (vc->vcore_state == VCORE_RUNNING &&
VCORE_EXIT_COUNT(vc) == 0) {
if (vc->vcore_state == VCORE_RUNNING && !VCORE_IS_EXITING(vc)) {
kvmppc_create_dtl_entry(vcpu, vc);
kvmppc_start_thread(vcpu);
trace_kvm_guest_enter(vcpu);

10
arch/powerpc/kvm/book3s_hv_builtin.c
View File

@ -115,11 +115,11 @@ long int kvmppc_rm_h_confer(struct kvm_vcpu *vcpu, int target,
int rv = H_SUCCESS; /* => don't yield */
set_bit(vcpu->arch.ptid, &vc->conferring_threads);
while ((get_tb() < stop) && (VCORE_EXIT_COUNT(vc) == 0)) {
threads_running = VCORE_ENTRY_COUNT(vc);
threads_ceded = hweight32(vc->napping_threads);
threads_conferring = hweight32(vc->conferring_threads);
if (threads_ceded + threads_conferring >= threads_running) {
while ((get_tb() < stop) && !VCORE_IS_EXITING(vc)) {
threads_running = VCORE_ENTRY_MAP(vc);
threads_ceded = vc->napping_threads;
threads_conferring = vc->conferring_threads;
if ((threads_ceded | threads_conferring) == threads_running) {
rv = H_TOO_HARD; /* => do yield */
break;
}

61
arch/powerpc/kvm/book3s_hv_rmhandlers.S
View File

@ -185,7 +185,7 @@ kvmppc_primary_no_guest:
or r3, r3, r0
stwcx. r3, 0, r6
bne 1b
/* order napping_threads update vs testing entry_exit_count */
/* order napping_threads update vs testing entry_exit_map */
isync
li r12, 0
lwz r7, VCORE_ENTRY_EXIT(r5)
@ -406,19 +406,21 @@ kvmppc_hv_entry:
* We don't have to lock against concurrent tlbies,
* but we do have to coordinate across hardware threads.
*/
/* Increment entry count iff exit count is zero. */
ld r5,HSTATE_KVM_VCORE(r13)
addi r9,r5,VCORE_ENTRY_EXIT
21: lwarx r3,0,r9
cmpwi r3,0x100 /* any threads starting to exit? */
/* Set bit in entry map iff exit map is zero. */
ld r5, HSTATE_KVM_VCORE(r13)
li r7, 1
lbz r6, HSTATE_PTID(r13)
sld r7, r7, r6
addi r9, r5, VCORE_ENTRY_EXIT
21: lwarx r3, 0, r9
cmpwi r3, 0x100 /* any threads starting to exit? */
bge secondary_too_late /* if so we're too late to the party */
addi r3,r3,1
stwcx. r3,0,r9
or r3, r3, r7
stwcx. r3, 0, r9
bne 21b
/* Primary thread switches to guest partition. */
ld r9,VCORE_KVM(r5) /* pointer to struct kvm */
lbz r6,HSTATE_PTID(r13)
cmpwi r6,0
bne 20f
ld r6,KVM_SDR1(r9)
@ -1477,13 +1479,16 @@ kvmhv_do_exit: /* r12 = trap, r13 = paca */
* We don't have to lock against tlbies but we do
* have to coordinate the hardware threads.
*/
/* Increment the threads-exiting-guest count in the 0xff00
bits of vcore->entry_exit_count */
ld r5,HSTATE_KVM_VCORE(r13)
addi r6,r5,VCORE_ENTRY_EXIT
41: lwarx r3,0,r6
addi r0,r3,0x100
stwcx. r0,0,r6
/* Set our bit in the threads-exiting-guest map in the 0xff00
bits of vcore->entry_exit_map */
ld r5, HSTATE_KVM_VCORE(r13)
lbz r4, HSTATE_PTID(r13)
li r7, 0x100
sld r7, r7, r4
addi r6, r5, VCORE_ENTRY_EXIT
41: lwarx r3, 0, r6
or r0, r3, r7
stwcx. r0, 0, r6
bne 41b
isync /* order stwcx. vs. reading napping_threads */
@ -1492,9 +1497,9 @@ kvmhv_do_exit: /* r12 = trap, r13 = paca */
* up to the kernel or qemu; we can't handle it in real mode.
* Thus we have to do a partition switch, so we have to
* collect the other threads, if we are the first thread
* to take an interrupt. To do this, we set the HDEC to 0,
* which causes an HDEC interrupt in all threads within 2ns
* because the HDEC register is shared between all 4 threads.
* to take an interrupt. To do this, we send a message or
* IPI to all the threads that have their bit set in the entry
* map in vcore->entry_exit_map (other than ourselves).
* However, we don't need to bother if this is an HDEC
* interrupt, since the other threads will already be on their
* way here in that case.
@ -1503,17 +1508,8 @@ kvmhv_do_exit: /* r12 = trap, r13 = paca */
bge 43f
cmpwi r12,BOOK3S_INTERRUPT_HV_DECREMENTER
beq 43f
li r0,0
mtspr SPRN_HDEC,r0
/*
* Send an IPI to any napping threads, since an HDEC interrupt
* doesn't wake CPUs up from nap.
*/
lwz r3,VCORE_NAPPING_THREADS(r5)
lbz r4,HSTATE_PTID(r13)
li r0,1
sld r0,r0,r4
srwi r0,r7,8
andc. r3,r3,r0 /* no sense IPI'ing ourselves */
beq 43f
/* Order entry/exit update vs. IPIs */
@ -2091,12 +2087,11 @@ _GLOBAL(kvmppc_h_cede) /* r3 = vcpu pointer, r11 = msr, r13 = paca */
addi r6,r5,VCORE_NAPPING_THREADS
31: lwarx r4,0,r6
or r4,r4,r0
PPC_POPCNTW(R7,R4)
cmpw r7,r8
bge kvm_cede_exit
cmpw r4,r8
beq kvm_cede_exit
stwcx. r4,0,r6
bne 31b
/* order napping_threads update vs testing entry_exit_count */
/* order napping_threads update vs testing entry_exit_map */
isync
li r0,NAPPING_CEDE
stb r0,HSTATE_NAPPING(r13)