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KVM: PPC: Book3S HV: Enable guests to use large decrementer mode on POWER9 

This allows userspace (e.g. QEMU) to enable large decrementer mode for
the guest when running on a POWER9 host, by setting the LPCR_LD bit in
the guest LPCR value.  With this, the guest exit code saves 64 bits of
the guest DEC value on exit.  Other places that use the guest DEC
value check the LPCR_LD bit in the guest LPCR value, and if it is set,
omit the 32-bit sign extension that would otherwise be done.

This doesn't change the DEC emulation used by PR KVM because PR KVM
is not supported on POWER9 yet.

This is partly based on an earlier patch by Oliver O'Halloran.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This commit is contained in:
Paul Mackerras 2017-05-22 16:55:16 +10:00
parent 3d3efb68c1
commit 1bc3fe818c
4 changed files with 33 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/powerpc/include/asm/kvm_host.h
View File

@ -579,7 +579,7 @@ struct kvm_vcpu_arch {
ulong mcsrr0;
ulong mcsrr1;
ulong mcsr;
u32 dec;
ulong dec;
#ifdef CONFIG_BOOKE
u32 decar;
#endif

6
arch/powerpc/kvm/book3s_hv.c
View File

@ -1143,6 +1143,12 @@ static void kvmppc_set_lpcr(struct kvm_vcpu *vcpu, u64 new_lpcr,
mask = LPCR_DPFD | LPCR_ILE | LPCR_TC;
if (cpu_has_feature(CPU_FTR_ARCH_207S))
mask |= LPCR_AIL;
/*
* On POWER9, allow userspace to enable large decrementer for the
* guest, whether or not the host has it enabled.
*/
if (cpu_has_feature(CPU_FTR_ARCH_300))
mask |= LPCR_LD;
/* Broken 32-bit version of LPCR must not clear top bits */
if (preserve_top32)

29
arch/powerpc/kvm/book3s_hv_rmhandlers.S
View File

@ -936,7 +936,7 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_ARCH_300)
mftb r7
subf r3,r7,r8
mtspr SPRN_DEC,r3
stw r3,VCPU_DEC(r4)
std r3,VCPU_DEC(r4)
ld r5, VCPU_SPRG0(r4)
ld r6, VCPU_SPRG1(r4)
@ -1048,7 +1048,13 @@ kvmppc_cede_reentry: /* r4 = vcpu, r13 = paca */
li r0, BOOK3S_INTERRUPT_EXTERNAL
bne cr1, 12f
mfspr r0, SPRN_DEC
cmpwi r0, 0
BEGIN_FTR_SECTION
/* On POWER9 check whether the guest has large decrementer enabled */
andis. r8, r8, LPCR_LD@h
bne 15f
END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
extsw r0, r0
15: cmpdi r0, 0
li r0, BOOK3S_INTERRUPT_DECREMENTER
bge 5f
@ -1475,12 +1481,18 @@ mc_cont:
mtspr SPRN_SPURR,r4
/* Save DEC */
ld r3, HSTATE_KVM_VCORE(r13)
mfspr r5,SPRN_DEC
mftb r6
/* On P9, if the guest has large decr enabled, don't sign extend */
BEGIN_FTR_SECTION
ld r4, VCORE_LPCR(r3)
andis. r4, r4, LPCR_LD@h
bne 16f
END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
extsw r5,r5
add r5,r5,r6
16: add r5,r5,r6
/* r5 is a guest timebase value here, convert to host TB */
ld r3,HSTATE_KVM_VCORE(r13)
ld r4,VCORE_TB_OFFSET(r3)
subf r5,r4,r5
std r5,VCPU_DEC_EXPIRES(r9)
@ -2402,8 +2414,15 @@ END_FTR_SECTION_IFSET(CPU_FTR_TM)
mfspr r3, SPRN_DEC
mfspr r4, SPRN_HDEC
mftb r5
BEGIN_FTR_SECTION
/* On P9 check whether the guest has large decrementer mode enabled */
ld r6, HSTATE_KVM_VCORE(r13)
ld r6, VCORE_LPCR(r6)
andis. r6, r6, LPCR_LD@h
bne 68f
END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
extsw r3, r3
EXTEND_HDEC(r4)
68: EXTEND_HDEC(r4)
cmpd r3, r4
ble 67f
mtspr SPRN_DEC, r4

4
arch/powerpc/kvm/emulate.c
View File

@ -39,7 +39,7 @@ void kvmppc_emulate_dec(struct kvm_vcpu *vcpu)
unsigned long dec_nsec;
unsigned long long dec_time;
pr_debug("mtDEC: %x\n", vcpu->arch.dec);
pr_debug("mtDEC: %lx\n", vcpu->arch.dec);
hrtimer_try_to_cancel(&vcpu->arch.dec_timer);
#ifdef CONFIG_PPC_BOOK3S
@ -109,7 +109,7 @@ static int kvmppc_emulate_mtspr(struct kvm_vcpu *vcpu, int sprn, int rs)
case SPRN_TBWU: break;
case SPRN_DEC:
vcpu->arch.dec = spr_val;
vcpu->arch.dec = (u32) spr_val;
kvmppc_emulate_dec(vcpu);
break;