[PATCH] KVM: PPC: Book3S HV: Use feature flag CPU_FTR_P9_TIDR when accessing TIDR

[PATCH] KVM: PPC: Book3S HV: Use feature flag CPU_FTR_P9_TIDR when accessing TIDR

[Cédric Le Goater]

The TIDR register is only available on POWER9 systems and code
accessing this register is not always protected by the CPU_FTR_P9_TIDR
flag. Fix that to make sure POWER10 systems won't use it as TIDR has
been removed.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
---
 arch/powerpc/kvm/book3s_hv.c            | 23 +++++++++++++++++------
 arch/powerpc/kvm/book3s_hv_rmhandlers.S | 16 ++++++++++++----
 2 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index d64a2dc1ccca..3e5410f27a2a 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1755,7 +1755,10 @@ static int kvmppc_get_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
 		*val = get_reg_val(id, vcpu->arch.wort);
 		break;
 	case KVM_REG_PPC_TIDR:
-		*val = get_reg_val(id, vcpu->arch.tid);
+		if (cpu_has_feature(CPU_FTR_P9_TIDR))
+			*val = get_reg_val(id, vcpu->arch.tid);
+		else
+			r = -ENXIO;
 		break;
 	case KVM_REG_PPC_PSSCR:
 		*val = get_reg_val(id, vcpu->arch.psscr);
@@ -1972,7 +1975,10 @@ static int kvmppc_set_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
 		vcpu->arch.wort = set_reg_val(id, *val);
 		break;
 	case KVM_REG_PPC_TIDR:
-		vcpu->arch.tid = set_reg_val(id, *val);
+		if (cpu_has_feature(CPU_FTR_P9_TIDR))
+			vcpu->arch.tid = set_reg_val(id, *val);
+		else
+			r = -ENXIO;
 		break;
 	case KVM_REG_PPC_PSSCR:
 		vcpu->arch.psscr = set_reg_val(id, *val) & PSSCR_GUEST_VIS;
@@ -3526,13 +3532,15 @@ int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit,
 {
 	struct kvmppc_vcore *vc = vcpu->arch.vcore;
 	unsigned long host_dscr = mfspr(SPRN_DSCR);
-	unsigned long host_tidr = mfspr(SPRN_TIDR);
+	unsigned long host_tidr;
 	unsigned long host_iamr = mfspr(SPRN_IAMR);
 	unsigned long host_amr = mfspr(SPRN_AMR);
 	s64 dec;
 	u64 tb;
 	int trap, save_pmu;
 
+	if (cpu_has_feature(CPU_FTR_P9_TIDR))
+		host_tidr = mfspr(SPRN_TIDR);
 	dec = mfspr(SPRN_DEC);
 	tb = mftb();
 	if (dec < 512)
@@ -3579,7 +3587,8 @@ int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit,
 	mtspr(SPRN_EBBRR, vcpu->arch.ebbrr);
 	mtspr(SPRN_BESCR, vcpu->arch.bescr);
 	mtspr(SPRN_WORT, vcpu->arch.wort);
-	mtspr(SPRN_TIDR, vcpu->arch.tid);
+	if (cpu_has_feature(CPU_FTR_P9_TIDR))
+		mtspr(SPRN_TIDR, vcpu->arch.tid);
 	mtspr(SPRN_DAR, vcpu->arch.shregs.dar);
 	mtspr(SPRN_DSISR, vcpu->arch.shregs.dsisr);
 	mtspr(SPRN_AMR, vcpu->arch.amr);
@@ -3653,7 +3662,8 @@ int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit,
 	vcpu->arch.ebbrr = mfspr(SPRN_EBBRR);
 	vcpu->arch.bescr = mfspr(SPRN_BESCR);
 	vcpu->arch.wort = mfspr(SPRN_WORT);
-	vcpu->arch.tid = mfspr(SPRN_TIDR);
+	if (cpu_has_feature(CPU_FTR_P9_TIDR))
+		vcpu->arch.tid = mfspr(SPRN_TIDR);
 	vcpu->arch.amr = mfspr(SPRN_AMR);
 	vcpu->arch.uamor = mfspr(SPRN_UAMOR);
 	vcpu->arch.dscr = mfspr(SPRN_DSCR);
@@ -3662,7 +3672,8 @@ int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit,
 	mtspr(SPRN_WORT, 0);
 	mtspr(SPRN_UAMOR, 0);
 	mtspr(SPRN_DSCR, host_dscr);
-	mtspr(SPRN_TIDR, host_tidr);
+	if (cpu_has_feature(CPU_FTR_P9_TIDR))
+		mtspr(SPRN_TIDR, host_tidr);
 	mtspr(SPRN_IAMR, host_iamr);
 	mtspr(SPRN_PSPB, 0);
 
diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index 71943892c81c..64e454656749 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -697,9 +697,11 @@ kvmppc_got_guest:
 	/* Save host values of some registers */
 BEGIN_FTR_SECTION
 	mfspr	r5, SPRN_TIDR
+	std	r5, STACK_SLOT_TID(r1)
+END_FTR_SECTION_IFSET(CPU_FTR_P9_TIDR)
+BEGIN_FTR_SECTION
 	mfspr	r6, SPRN_PSSCR
 	mfspr	r7, SPRN_PID
-	std	r5, STACK_SLOT_TID(r1)
 	std	r6, STACK_SLOT_PSSCR(r1)
 	std	r7, STACK_SLOT_PID(r1)
 	mfspr	r5, SPRN_HFSCR
@@ -835,13 +837,15 @@ BEGIN_FTR_SECTION
 	nop
 FTR_SECTION_ELSE
 	/* POWER9-only registers */
+BEGIN_FTR_SECTION_NESTED(96);
 	ld	r5, VCPU_TID(r4)
+	mtspr	SPRN_TIDR, r5
+END_FTR_SECTION_NESTED_IFSET(CPU_FTR_P9_TIDR, 96)
 	ld	r6, VCPU_PSSCR(r4)
 	lbz	r8, HSTATE_FAKE_SUSPEND(r13)
 	oris	r6, r6, PSSCR_EC@h	/* This makes stop trap to HV */
 	rldimi	r6, r8, PSSCR_FAKE_SUSPEND_LG, 63 - PSSCR_FAKE_SUSPEND_LG
 	ld	r7, VCPU_HFSCR(r4)
-	mtspr	SPRN_TIDR, r5
 	mtspr	SPRN_PSSCR, r6
 	mtspr	SPRN_HFSCR, r7
 ALT_FTR_SECTION_END_IFCLR(CPU_FTR_ARCH_300)
@@ -1637,9 +1641,11 @@ BEGIN_FTR_SECTION
 	std	r7, VCPU_CSIGR(r9)
 	std	r8, VCPU_TACR(r9)
 FTR_SECTION_ELSE
+BEGIN_FTR_SECTION_NESTED(96);
 	mfspr	r5, SPRN_TIDR
-	mfspr	r6, SPRN_PSSCR
 	std	r5, VCPU_TID(r9)
+END_FTR_SECTION_NESTED_IFSET(CPU_FTR_P9_TIDR, 96)
+	mfspr	r6, SPRN_PSSCR
 	rldicl	r6, r6, 4, 50		/* r6 &= PSSCR_GUEST_VIS */
 	rotldi	r6, r6, 60
 	std	r6, VCPU_PSSCR(r9)
@@ -1771,9 +1777,11 @@ BEGIN_FTR_SECTION
 END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 BEGIN_FTR_SECTION
 	ld	r5, STACK_SLOT_TID(r1)
+	mtspr	SPRN_TIDR, r5
+END_FTR_SECTION_IFSET(CPU_FTR_P9_TIDR)
+BEGIN_FTR_SECTION
 	ld	r6, STACK_SLOT_PSSCR(r1)
 	ld	r7, STACK_SLOT_PID(r1)
-	mtspr	SPRN_TIDR, r5
 	mtspr	SPRN_PSSCR, r6
 	mtspr	SPRN_PID, r7
 END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
-- 
2.25.4

Re: [PATCH] KVM: PPC: Book3S HV: Use feature flag CPU_FTR_P9_TIDR when accessing TIDR

[Paul Mackerras]

On Tue, Jun 23, 2020 at 06:50:27PM +0200, Cédric Le Goater wrote:
> The TIDR register is only available on POWER9 systems and code
> accessing this register is not always protected by the CPU_FTR_P9_TIDR
> flag. Fix that to make sure POWER10 systems won't use it as TIDR has
> been removed.

I'm concerned about what this patch would do if we are trying to
migrate from a P9 guest to a guest on P10 in P9-compat mode, in that
the destination QEMU would get an error on doing the SET_ONE_REG for
the TIDR.  I don't think the lack of TIDR is worth failing the
migration for given that TIDR only actually does anything if you are
using an accelerator, and KVM has never supported use of accelerators
in guests.  I'm cc'ing David Gibson for his comments on the
compatibility and migration issues.

In any case, given that both move to and move from TIDR will be no-ops
on P10 (for privileged code), I don't think there is a great urgency
for this patch.

Paul.

Re: [PATCH] KVM: PPC: Book3S HV: Use feature flag CPU_FTR_P9_TIDR when accessing TIDR

[David Gibson]

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On Tue, Jul 21, 2020 at 03:04:45PM +1000, Paul Mackerras wrote:
> On Tue, Jun 23, 2020 at 06:50:27PM +0200, Cédric Le Goater wrote:
> > The TIDR register is only available on POWER9 systems and code
> > accessing this register is not always protected by the CPU_FTR_P9_TIDR
> > flag. Fix that to make sure POWER10 systems won't use it as TIDR has
> > been removed.
> 
> I'm concerned about what this patch would do if we are trying to
> migrate from a P9 guest to a guest on P10 in P9-compat mode, in that
> the destination QEMU would get an error on doing the SET_ONE_REG for
> the TIDR.  I don't think the lack of TIDR is worth failing the
> migration for given that TIDR only actually does anything if you are
> using an accelerator, and KVM has never supported use of accelerators
> in guests.  I'm cc'ing David Gibson for his comments on the
> compatibility and migration issues.

Having thought about this a bit more, I don't think it matters.  We're
going to have to update qemu to handle POWER10 anyway.  If this causes
a problem, this would just add one small thing to whatever we need to
fix there.

> In any case, given that both move to and move from TIDR will be no-ops
> on P10 (for privileged code), I don't think there is a great urgency
> for this patch.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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