Use HFSCR facility disabling to implement demand faulting for EBB, 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.
Reviewed-by: Fabiano Rosas <farosas@xxxxxxxxxxxxx>
Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
---
arch/powerpc/include/asm/kvm_host.h | 1 +
arch/powerpc/kvm/book3s_hv.c | 16 +++++++++++++--
arch/powerpc/kvm/book3s_hv_p9_entry.c | 28 +++++++++++++++++++++------
3 files changed, 37 insertions(+), 8 deletions(-)
diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index f105eaeb4521..1c00c4a565f5 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -580,6 +580,7 @@ struct kvm_vcpu_arch {
ulong cfar;
ulong ppr;
u32 pspb;
+ u8 load_ebb;
ulong fscr;
ulong shadow_fscr;
ulong ebbhr;
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 47ccea5ffba2..dd8199a423cf 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1441,6 +1441,16 @@ static int kvmppc_pmu_unavailable(struct kvm_vcpu *vcpu)
return RESUME_GUEST;
}
+static int kvmppc_ebb_unavailable(struct kvm_vcpu *vcpu)
+{
+ if (!(vcpu->arch.hfscr_permitted & HFSCR_EBB))
+ return EMULATE_FAIL;
+
+ vcpu->arch.hfscr |= HFSCR_EBB;
+
+ return RESUME_GUEST;
+}
+
static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu,
struct task_struct *tsk)
{
@@ -1735,6 +1745,8 @@ XXX benchmark guest exits
r = kvmppc_emulate_doorbell_instr(vcpu);
if (cause == FSCR_PM_LG)
r = kvmppc_pmu_unavailable(vcpu);
+ if (cause == FSCR_EBB_LG)
+ r = kvmppc_ebb_unavailable(vcpu);
}
if (r == EMULATE_FAIL) {
kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
@@ -2751,9 +2763,9 @@ static int kvmppc_core_vcpu_create_hv(struct kvm_vcpu *vcpu)
vcpu->arch.hfscr_permitted = vcpu->arch.hfscr;
/*
- * PM is demand-faulted so start with it clear.
+ * PM, EBB is demand-faulted so start with it clear.
*/
- vcpu->arch.hfscr &= ~HFSCR_PM;
+ vcpu->arch.hfscr &= ~(HFSCR_PM | HFSCR_EBB);
kvmppc_mmu_book3s_hv_init(vcpu);
diff --git a/arch/powerpc/kvm/book3s_hv_p9_entry.c b/arch/powerpc/kvm/book3s_hv_p9_entry.c
index c4e93167d120..f68a3d107d04 100644
--- a/arch/powerpc/kvm/book3s_hv_p9_entry.c
+++ b/arch/powerpc/kvm/book3s_hv_p9_entry.c
@@ -224,9 +224,12 @@ static void load_spr_state(struct kvm_vcpu *vcpu,
struct p9_host_os_sprs *host_os_sprs)
{
mtspr(SPRN_TAR, vcpu->arch.tar);
- mtspr(SPRN_EBBHR, vcpu->arch.ebbhr);
- mtspr(SPRN_EBBRR, vcpu->arch.ebbrr);
- mtspr(SPRN_BESCR, vcpu->arch.bescr);
+
+ if (vcpu->arch.hfscr & HFSCR_EBB) {
+ mtspr(SPRN_EBBHR, vcpu->arch.ebbhr);
+ mtspr(SPRN_EBBRR, vcpu->arch.ebbrr);
+ mtspr(SPRN_BESCR, vcpu->arch.bescr);
+ }
if (!cpu_has_feature(CPU_FTR_ARCH_31))
mtspr(SPRN_TIDR, vcpu->arch.tid);
@@ -257,9 +260,22 @@ static void load_spr_state(struct kvm_vcpu *vcpu,
static void store_spr_state(struct kvm_vcpu *vcpu)
{
vcpu->arch.tar = mfspr(SPRN_TAR);
- vcpu->arch.ebbhr = mfspr(SPRN_EBBHR);
- vcpu->arch.ebbrr = mfspr(SPRN_EBBRR);
- vcpu->arch.bescr = mfspr(SPRN_BESCR);
+
+ if (vcpu->arch.hfscr & HFSCR_EBB) {
+ vcpu->arch.ebbhr = mfspr(SPRN_EBBHR);
+ vcpu->arch.ebbrr = mfspr(SPRN_EBBRR);
+ vcpu->arch.bescr = mfspr(SPRN_BESCR);
+ /*
+ * This is like load_fp in context switching, turn off the
+ * facility after it wraps the u8 to try avoiding saving
+ * and restoring the registers each partition switch.
+ */
+ if (!vcpu->arch.nested) {
+ vcpu->arch.load_ebb++;
+ if (!vcpu->arch.load_ebb)
+ vcpu->arch.hfscr &= ~HFSCR_EBB;
+ }
+ }
if (!cpu_has_feature(CPU_FTR_ARCH_31))
vcpu->arch.tid = mfspr(SPRN_TIDR);
--
2.23.0
