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KVM: PPC: Book3S HV P9: Demand fault EBB facility registers

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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.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-37-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2021-11-23 19:52:14 +10:00 committed by Michael Ellerman
parent 34e02d555d
commit a3e18ca8ab
3 changed files with 37 additions and 8 deletions
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1
arch/powerpc/include/asm/kvm_host.h
View File

@ -579,6 +579,7 @@ struct kvm_vcpu_arch {
ulong cfar;
ulong ppr;
u32 pspb;
u8 load_ebb;
ulong fscr;
ulong shadow_fscr;
ulong ebbhr;

16
arch/powerpc/kvm/book3s_hv.c
View File

@ -1436,6 +1436,16 @@ 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)
{
@ -1727,6 +1737,8 @@ static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu,
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);
@ -2771,9 +2783,9 @@ 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);

28
arch/powerpc/kvm/book3s_hv_p9_entry.c
View File

@ -232,9 +232,12 @@ 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_P9_TIDR))
mtspr(SPRN_TIDR, vcpu->arch.tid);
@ -265,9 +268,22 @@ 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_P9_TIDR))
vcpu->arch.tid = mfspr(SPRN_TIDR);