Re: [RFC PATCH 35/43] KVM: PPC: Book3S HV P9: Demand fault TM facility registers
Nicholas Piggin writes:
> Use HFSCR facility disabling to implement demand faulting for TM, with
> a hysteresis counter similar to the load_fp etc counters in context
> switching that implement the equivalent demand faulting for userspace
> facilities.
>
> This speeds up guest entry/exit by avoiding the register save/restore
> when a guest is not frequently using them. When a guest does use them
> often, there will be some additional demand fault overhead, but these
> are not commonly used facilities.
>
> -304 cycles (6681) POWER9 virt-mode NULL hcall with the previous patch
>
> Signed-off-by: Nicholas Piggin
Reviewed-by: Fabiano Rosas
> ---
> arch/powerpc/include/asm/kvm_host.h | 1 +
> arch/powerpc/kvm/book3s_hv.c | 21 +
> arch/powerpc/kvm/book3s_hv_nested.c | 2 +-
> arch/powerpc/kvm/book3s_hv_p9_entry.c | 18 --
> 4 files changed, 31 insertions(+), 11 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/kvm_host.h
> b/arch/powerpc/include/asm/kvm_host.h
> index bee95106c1f2..d79f0b1b1578 100644
> --- a/arch/powerpc/include/asm/kvm_host.h
> +++ b/arch/powerpc/include/asm/kvm_host.h
> @@ -586,6 +586,7 @@ struct kvm_vcpu_arch {
> ulong ppr;
> u32 pspb;
> u8 load_ebb;
> + u8 load_tm;
> ulong fscr;
> ulong shadow_fscr;
> ulong ebbhr;
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 99e9da078e7d..2430725f29f7 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -1373,6 +1373,13 @@ static int kvmppc_ebb_unavailable(struct kvm_vcpu
> *vcpu)
> return RESUME_GUEST;
> }
>
> +static int kvmppc_tm_unavailable(struct kvm_vcpu *vcpu)
> +{
> + vcpu->arch.hfscr |= HFSCR_TM;
> +
> + return RESUME_GUEST;
> +}
> +
> static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu,
>struct task_struct *tsk)
> {
> @@ -1654,6 +1661,8 @@ XXX benchmark guest exits
> r = kvmppc_pmu_unavailable(vcpu);
> if (cause == FSCR_EBB_LG)
> r = kvmppc_ebb_unavailable(vcpu);
> + if (cause == FSCR_TM_LG)
> + r = kvmppc_tm_unavailable(vcpu);
> }
> if (r == EMULATE_FAIL) {
> kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
> @@ -1775,6 +1784,8 @@ static int kvmppc_handle_nested_exit(struct kvm_vcpu
> *vcpu)
> r = kvmppc_pmu_unavailable(vcpu);
> if (cause == FSCR_EBB_LG && (vcpu->arch.nested_hfscr &
> HFSCR_EBB))
> r = kvmppc_ebb_unavailable(vcpu);
> + if (cause == FSCR_TM_LG && (vcpu->arch.nested_hfscr & HFSCR_TM))
> + r = kvmppc_tm_unavailable(vcpu);
>
> if (r == EMULATE_FAIL)
> r = RESUME_HOST;
> @@ -3737,8 +3748,9 @@ static int kvmhv_vcpu_entry_p9_nested(struct kvm_vcpu
> *vcpu, u64 time_limit, uns
> msr |= MSR_VEC;
> if (cpu_has_feature(CPU_FTR_VSX))
> msr |= MSR_VSX;
> - if (cpu_has_feature(CPU_FTR_TM) ||
> - cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST))
> + if ((cpu_has_feature(CPU_FTR_TM) ||
> + cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST)) &&
> + (vcpu->arch.hfscr & HFSCR_TM))
> msr |= MSR_TM;
> msr = msr_check_and_set(msr);
>
> @@ -4453,8 +4465,9 @@ static int kvmppc_vcpu_run_hv(struct kvm_vcpu *vcpu)
> msr |= MSR_VEC;
> if (cpu_has_feature(CPU_FTR_VSX))
> msr |= MSR_VSX;
> - if (cpu_has_feature(CPU_FTR_TM) ||
> - cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST))
> + if ((cpu_has_feature(CPU_FTR_TM) ||
> + cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST)) &&
> + (vcpu->arch.hfscr & HFSCR_TM))
> msr |= MSR_TM;
> msr = msr_check_and_set(msr);
>
> diff --git a/arch/powerpc/kvm/book3s_hv_nested.c
> b/arch/powerpc/kvm/book3s_hv_nested.c
> index ee8668f056f9..5a534f7924f2 100644
> --- a/arch/powerpc/kvm/book3s_hv_nested.c
> +++ b/arch/powerpc/kvm/book3s_hv_nested.c
> @@ -168,7 +168,7 @@ static void sanitise_hv_regs(struct kvm_vcpu *vcpu,
> struct hv_guest_state *hr)
>* but preserve the interrupt cause field and facilities that might
>* be disabled for demand faulting in the L1.
>*/
> - hr->hfscr &= (HFSCR_INTR_CAUSE | HFSCR_PM | HFSCR_EBB |
> + hr->hfscr &= (HFSCR_INTR_CAUSE | HFSCR_PM | HFSCR_TM | HFSCR_EBB |
> vcpu->arch.hfscr);
>
> /* Don't let data address watchpoint match in hypervisor state */
> diff --git a/arch/powerpc/kvm/book3s_hv_p9_entry.c
> b/arch/powerpc/kvm/book3s_hv_p9_entry.c
> index cf41261daa97..653f2765a399 100644
> --- a/arch/powerpc/kvm/book3s_hv_p9_entry.c
> +++ b/arch/powerpc/kvm/book3s_hv_p9_entry.c
> @@ -284,8 +284,9 @@ static void store_spr_state(struct kvm_vcpu *vcpu)
> void
[RFC PATCH 35/43] KVM: PPC: Book3S HV P9: Demand fault TM facility registers
Use HFSCR facility disabling to implement demand faulting for TM, with
a hysteresis counter similar to the load_fp etc counters in context
switching that implement the equivalent demand faulting for userspace
facilities.
This speeds up guest entry/exit by avoiding the register save/restore
when a guest is not frequently using them. When a guest does use them
often, there will be some additional demand fault overhead, but these
are not commonly used facilities.
-304 cycles (6681) POWER9 virt-mode NULL hcall with the previous patch
Signed-off-by: Nicholas Piggin
---
arch/powerpc/include/asm/kvm_host.h | 1 +
arch/powerpc/kvm/book3s_hv.c | 21 +
arch/powerpc/kvm/book3s_hv_nested.c | 2 +-
arch/powerpc/kvm/book3s_hv_p9_entry.c | 18 --
4 files changed, 31 insertions(+), 11 deletions(-)
diff --git a/arch/powerpc/include/asm/kvm_host.h
b/arch/powerpc/include/asm/kvm_host.h
index bee95106c1f2..d79f0b1b1578 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -586,6 +586,7 @@ struct kvm_vcpu_arch {
ulong ppr;
u32 pspb;
u8 load_ebb;
+ u8 load_tm;
ulong fscr;
ulong shadow_fscr;
ulong ebbhr;
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 99e9da078e7d..2430725f29f7 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1373,6 +1373,13 @@ static int kvmppc_ebb_unavailable(struct kvm_vcpu *vcpu)
return RESUME_GUEST;
}
+static int kvmppc_tm_unavailable(struct kvm_vcpu *vcpu)
+{
+ vcpu->arch.hfscr |= HFSCR_TM;
+
+ return RESUME_GUEST;
+}
+
static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu,
struct task_struct *tsk)
{
@@ -1654,6 +1661,8 @@ XXX benchmark guest exits
r = kvmppc_pmu_unavailable(vcpu);
if (cause == FSCR_EBB_LG)
r = kvmppc_ebb_unavailable(vcpu);
+ if (cause == FSCR_TM_LG)
+ r = kvmppc_tm_unavailable(vcpu);
}
if (r == EMULATE_FAIL) {
kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
@@ -1775,6 +1784,8 @@ static int kvmppc_handle_nested_exit(struct kvm_vcpu
*vcpu)
r = kvmppc_pmu_unavailable(vcpu);
if (cause == FSCR_EBB_LG && (vcpu->arch.nested_hfscr &
HFSCR_EBB))
r = kvmppc_ebb_unavailable(vcpu);
+ if (cause == FSCR_TM_LG && (vcpu->arch.nested_hfscr & HFSCR_TM))
+ r = kvmppc_tm_unavailable(vcpu);
if (r == EMULATE_FAIL)
r = RESUME_HOST;
@@ -3737,8 +3748,9 @@ static int kvmhv_vcpu_entry_p9_nested(struct kvm_vcpu
*vcpu, u64 time_limit, uns
msr |= MSR_VEC;
if (cpu_has_feature(CPU_FTR_VSX))
msr |= MSR_VSX;
- if (cpu_has_feature(CPU_FTR_TM) ||
- cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST))
+ if ((cpu_has_feature(CPU_FTR_TM) ||
+ cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST)) &&
+ (vcpu->arch.hfscr & HFSCR_TM))
msr |= MSR_TM;
msr = msr_check_and_set(msr);
@@ -4453,8 +4465,9 @@ static int kvmppc_vcpu_run_hv(struct kvm_vcpu *vcpu)
msr |= MSR_VEC;
if (cpu_has_feature(CPU_FTR_VSX))
msr |= MSR_VSX;
- if (cpu_has_feature(CPU_FTR_TM) ||
- cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST))
+ if ((cpu_has_feature(CPU_FTR_TM) ||
+ cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST)) &&
+ (vcpu->arch.hfscr & HFSCR_TM))
msr |= MSR_TM;
msr = msr_check_and_set(msr);
diff --git a/arch/powerpc/kvm/book3s_hv_nested.c
b/arch/powerpc/kvm/book3s_hv_nested.c
index ee8668f056f9..5a534f7924f2 100644
--- a/arch/powerpc/kvm/book3s_hv_nested.c
+++ b/arch/powerpc/kvm/book3s_hv_nested.c
@@ -168,7 +168,7 @@ static void sanitise_hv_regs(struct kvm_vcpu *vcpu, struct
hv_guest_state *hr)
* but preserve the interrupt cause field and facilities that might
* be disabled for demand faulting in the L1.
*/
- hr->hfscr &= (HFSCR_INTR_CAUSE | HFSCR_PM | HFSCR_EBB |
+ hr->hfscr &= (HFSCR_INTR_CAUSE | HFSCR_PM | HFSCR_TM | HFSCR_EBB |
vcpu->arch.hfscr);
/* Don't let data address watchpoint match in hypervisor state */
diff --git a/arch/powerpc/kvm/book3s_hv_p9_entry.c
b/arch/powerpc/kvm/book3s_hv_p9_entry.c
index cf41261daa97..653f2765a399 100644
--- a/arch/powerpc/kvm/book3s_hv_p9_entry.c
+++ b/arch/powerpc/kvm/book3s_hv_p9_entry.c
@@ -284,8 +284,9 @@ static void store_spr_state(struct kvm_vcpu *vcpu)
void load_vcpu_state(struct kvm_vcpu *vcpu,
struct p9_host_os_sprs *host_os_sprs)
{
- if (cpu_has_feature(CPU_FTR_TM) ||
- cpu_has_feat
