[PATCH V2 0/2] KVM: PPC: Book3S HV: Support POWER9's large decrementer mode

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[PATCH V2 0/2] KVM: PPC: Book3S HV: Support POWER9's large decrementer mode

From: Paul Mackerras <hidden>
Date: 2017-05-29 00:09:49

One of the new features of POWER9 is that the decrementer (the
facility that provides an interrupt after a programmable length of
time) has been increased in size from 32 bits to 56 bits, allowing
time intervals of up to about 814 days, compared to 4 seconds
previously.  This patch series adds support for the large decrementer
mode to HV KVM.  There is already code in the host kernel to enable
large decrementer mode for the host, which means that some of the KVM
entry/exit code is currently incorrect; the first patch fixes that.
The second patch allows userspace to enable large decrementer mode for
the guest, by setting the appropriate bit in the guest LPCR value.

Changes in v2: use the presence of the ibm,dec-bits property to set
the CPU_FTR_LARGE_DEC bit rather than the ibm,pa-features property,
because QEMU already sets the large decrementer bit in the
ibm,pa-features property (correctly, since ibm,pa-features describes
the capabilities of the CPU hardware, not the settings established by
the host) but does not currently enable large decrementer mode for the
guest.

Paul.
---
 arch/powerpc/include/asm/cputable.h     |  4 ++-
 arch/powerpc/include/asm/kvm_host.h     |  2 +-
 arch/powerpc/kernel/prom.c              |  1 +
 arch/powerpc/kernel/time.c              |  7 ++---
 arch/powerpc/kvm/book3s_hv.c            |  2 ++
 arch/powerpc/kvm/book3s_hv_interrupts.S |  2 ++
 arch/powerpc/kvm/book3s_hv_rmhandlers.S | 51 ++++++++++++++++++++++++++-------
 arch/powerpc/kvm/emulate.c              |  4 +--
 8 files changed, 54 insertions(+), 19 deletions(-)

[PATCH V2 2/2] KVM: PPC: Book3S HV: Enable guests to use large decrementer mode on POWER9

From: Paul Mackerras <hidden>
Date: 2017-05-29 00:09:49

This allows userspace (e.g. QEMU) to enable large decrementer mode
for the guest, 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 <redacted>
---
 arch/powerpc/include/asm/kvm_host.h     |  2 +-
 arch/powerpc/kvm/book3s_hv.c            |  2 ++
 arch/powerpc/kvm/book3s_hv_rmhandlers.S | 28 ++++++++++++++++++++++++----
 arch/powerpc/kvm/emulate.c              |  4 ++--
 4 files changed, 29 insertions(+), 7 deletions(-)

diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 9c51ac4..3f879c8 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h

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

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 42b7a4f..1f9c0ee 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c

@@ -1143,6 +1143,8 @@ 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;
+	if (cpu_has_feature(CPU_FTR_LARGE_DEC))
+		mask |= LPCR_LD;
 
 	/* Broken 32-bit version of LPCR must not clear top bits */
 	if (preserve_top32)

diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index bcb5401..e7a2c89 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S

@@ -916,7 +916,7 @@ 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)

@@ -1030,7 +1030,13 @@ 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

@@ -1457,12 +1463,18 @@ 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)

@@ -2374,7 +2386,15 @@ 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
+68:
 BEGIN_FTR_SECTION
 	extsw	r4, r4
 END_FTR_SECTION_IFSET(CPU_FTR_LARGE_DEC)

diff --git a/arch/powerpc/kvm/emulate.c b/arch/powerpc/kvm/emulate.c
index c873ffe..4d8b4d6 100644
--- a/arch/powerpc/kvm/emulate.c
+++ b/arch/powerpc/kvm/emulate.c

@@ -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;

-- 
2.7.4

[PATCH V2 1/2] KVM: PPC: Book3S HV: Cope with host using large decrementer mode

From: Paul Mackerras <hidden>
Date: 2017-05-29 00:09:49

POWER9 introduces a new mode for the decrementer register, called
large decrementer mode, in which the decrementer counter is 56 bits
wide rather than 32, and reads are sign-extended rather than
zero-extended.

Since KVM code reads and writes the host decrementer value in a few
places, it needs to be aware of the need to treat the decrementer
value as a 64-bit quantity, and only do a 32-bit sign extension when
large decrementer mode is not in effect.  To enable the sign extension
to be removed in large decrementer mode, we use a CPU feature bit to
indicate that large decrementer mode is in effect.  This CPU feature
bit is derived from the presence of the ibm,dec-bits property in the
cpu nodes of the firmware device tree.  This property is already set
by firmware in the device tree that the kernel uses when running as a
host.  We change the kernel timer code to use this bit and enable
large decrementer mode whenever it is set (even if firmware tells us
that the large decrementer mode only gives us 32 bits) so that we get
the sign extension in hardware.

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

Cc: stable@vger.kernel.org # v4.10+
Signed-off-by: Paul Mackerras <redacted>
---
 arch/powerpc/include/asm/cputable.h     |  4 +++-
 arch/powerpc/kernel/prom.c              |  1 +
 arch/powerpc/kernel/time.c              |  7 ++-----
 arch/powerpc/kvm/book3s_hv_interrupts.S |  2 ++
 arch/powerpc/kvm/book3s_hv_rmhandlers.S | 23 +++++++++++++++++------
 5 files changed, 25 insertions(+), 12 deletions(-)

diff --git a/arch/powerpc/include/asm/cputable.h b/arch/powerpc/include/asm/cputable.h
index c2d5095..99c3c56 100644
--- a/arch/powerpc/include/asm/cputable.h
+++ b/arch/powerpc/include/asm/cputable.h

@@ -216,6 +216,7 @@ enum {
 #define CPU_FTR_PMAO_BUG		LONG_ASM_CONST(0x1000000000000000)
 #define CPU_FTR_SUBCORE			LONG_ASM_CONST(0x2000000000000000)
 #define CPU_FTR_POWER9_DD1		LONG_ASM_CONST(0x4000000000000000)
+#define CPU_FTR_LARGE_DEC		LONG_ASM_CONST(0x8000000000000000)
 
 #ifndef __ASSEMBLY__

@@ -496,7 +497,8 @@ enum {
 	    (CPU_FTRS_POWER4 | CPU_FTRS_PPC970 | CPU_FTRS_POWER5 | \
 	     CPU_FTRS_POWER6 | CPU_FTRS_POWER7 | CPU_FTRS_POWER8E | \
 	     CPU_FTRS_POWER8 | CPU_FTRS_POWER8_DD1 | CPU_FTRS_CELL | \
-	     CPU_FTRS_PA6T | CPU_FTR_VSX | CPU_FTRS_POWER9 | CPU_FTRS_POWER9_DD1)
+	     CPU_FTRS_PA6T | CPU_FTR_VSX | CPU_FTRS_POWER9 | \
+	     CPU_FTRS_POWER9_DD1 | CPU_FTR_LARGE_DEC)
 #endif
 #else
 enum {

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 40c4887..987fcc5 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c

@@ -259,6 +259,7 @@ static struct feature_property {
 	{"ibm,dfp", 1, 0, PPC_FEATURE_HAS_DFP},
 	{"ibm,purr", 1, CPU_FTR_PURR, 0},
 	{"ibm,spurr", 1, CPU_FTR_SPURR, 0},
+	{"ibm,dec-bits", 32, CPU_FTR_LARGE_DEC, 0},
 #endif /* CONFIG_PPC64 */
 };

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 2b33cfa..5d13f06 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c

@@ -946,10 +946,7 @@ static void register_decrementer_clockevent(int cpu)
 
 static void enable_large_decrementer(void)
 {
-	if (!cpu_has_feature(CPU_FTR_ARCH_300))
-		return;
-
-	if (decrementer_max <= DECREMENTER_DEFAULT_MAX)
+	if (!cpu_has_feature(CPU_FTR_LARGE_DEC))
 		return;
 
 	/*

@@ -966,7 +963,7 @@ static void __init set_decrementer_max(void)
 	u32 bits = 32;
 
 	/* Prior to ISAv3 the decrementer is always 32 bit */
-	if (!cpu_has_feature(CPU_FTR_ARCH_300))
+	if (!cpu_has_feature(CPU_FTR_LARGE_DEC))
 		return;
 
 	cpu = of_find_node_by_type(NULL, "cpu");

diff --git a/arch/powerpc/kvm/book3s_hv_interrupts.S b/arch/powerpc/kvm/book3s_hv_interrupts.S
index 0fdc4a2..6e1d75f 100644
--- a/arch/powerpc/kvm/book3s_hv_interrupts.S
+++ b/arch/powerpc/kvm/book3s_hv_interrupts.S

@@ -124,7 +124,9 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 	mfspr	r8,SPRN_DEC
 	mftb	r7
 	mtspr	SPRN_HDEC,r8
+BEGIN_FTR_SECTION
 	extsw	r8,r8
+END_FTR_SECTION_IFCLR(CPU_FTR_LARGE_DEC)
 	add	r8,r8,r7
 	std	r8,HSTATE_DECEXP(r13)

diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index bdb3f76..bcb5401 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S

@@ -214,6 +214,8 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 kvmppc_primary_no_guest:
 	/* We handle this much like a ceded vcpu */
 	/* put the HDEC into the DEC, since HDEC interrupts don't wake us */
+	/* HDEC may be larger than DEC for arch >= v3.00, but since the */
+	/* HDEC value came from DEC in the first place, it will fit */
 	mfspr	r3, SPRN_HDEC
 	mtspr	SPRN_DEC, r3
 	/*

@@ -295,8 +297,11 @@ kvm_novcpu_wakeup:
 
 	/* See if our timeslice has expired (HDEC is negative) */
 	mfspr	r0, SPRN_HDEC
+BEGIN_FTR_SECTION
+	extsw	r0, r0
+END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_300)
 	li	r12, BOOK3S_INTERRUPT_HV_DECREMENTER
-	cmpwi	r0, 0
+	cmpdi	r0, 0
 	blt	kvm_novcpu_exit
 
 	/* Got an IPI but other vcpus aren't yet exiting, must be a latecomer */

@@ -390,8 +395,8 @@ kvm_secondary_got_guest:
 	lbz	r4, HSTATE_PTID(r13)
 	cmpwi	r4, 0
 	bne	63f
-	lis	r6, 0x7fff
-	ori	r6, r6, 0xffff
+	LOAD_REG_ADDR(r6, decrementer_max)
+	ld	r6, 0(r6)
 	mtspr	SPRN_HDEC, r6
 	/* and set per-LPAR registers, if doing dynamic micro-threading */
 	ld	r6, HSTATE_SPLIT_MODE(r13)

@@ -968,7 +973,10 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_ARCH_300)
 
 	/* Check if HDEC expires soon */
 	mfspr	r3, SPRN_HDEC
-	cmpwi	r3, 512		/* 1 microsecond */
+BEGIN_FTR_SECTION
+	extsw	r3, r3
+END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_300)
+	cmpdi	r3, 512		/* 1 microsecond */
 	blt	hdec_soon
 
 #ifdef CONFIG_KVM_XICS

@@ -2366,12 +2374,15 @@ END_FTR_SECTION_IFSET(CPU_FTR_TM)
 	mfspr	r3, SPRN_DEC
 	mfspr	r4, SPRN_HDEC
 	mftb	r5
-	cmpw	r3, r4
+	extsw	r3, r3
+BEGIN_FTR_SECTION
+	extsw	r4, r4
+END_FTR_SECTION_IFSET(CPU_FTR_LARGE_DEC)
+	cmpd	r3, r4
 	ble	67f
 	mtspr	SPRN_DEC, r4
 67:
 	/* save expiry time of guest decrementer */
-	extsw	r3, r3
 	add	r3, r3, r5
 	ld	r4, HSTATE_KVM_VCPU(r13)
 	ld	r5, HSTATE_KVM_VCORE(r13)

-- 
2.7.4

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