KVM: PPC: Allow book3s_hv guests to use SMT processor modes

This lifts the restriction that book3s_hv guests can only run one
hardware thread per core, and allows them to use up to 4 threads
per core on POWER7.  The host still has to run single-threaded.

This capability is advertised to qemu through a new KVM_CAP_PPC_SMT
capability.  The return value of the ioctl querying this capability
is the number of vcpus per virtual CPU core (vcore), currently 4.

To use this, the host kernel should be booted with all threads
active, and then all the secondary threads should be offlined.
This will put the secondary threads into nap mode.  KVM will then
wake them from nap mode and use them for running guest code (while
they are still offline).  To wake the secondary threads, we send
them an IPI using a new xics_wake_cpu() function, implemented in
arch/powerpc/sysdev/xics/icp-native.c.  In other words, at this stage
we assume that the platform has a XICS interrupt controller and
we are using icp-native.c to drive it.  Since the woken thread will
need to acknowledge and clear the IPI, we also export the base
physical address of the XICS registers using kvmppc_set_xics_phys()
for use in the low-level KVM book3s code.

When a vcpu is created, it is assigned to a virtual CPU core.
The vcore number is obtained by dividing the vcpu number by the
number of threads per core in the host.  This number is exported
to userspace via the KVM_CAP_PPC_SMT capability.  If qemu wishes
to run the guest in single-threaded mode, it should make all vcpu
numbers be multiples of the number of threads per core.

We distinguish three states of a vcpu: runnable (i.e., ready to execute
the guest), blocked (that is, idle), and busy in host.  We currently
implement a policy that the vcore can run only when all its threads
are runnable or blocked.  This way, if a vcpu needs to execute elsewhere
in the kernel or in qemu, it can do so without being starved of CPU
by the other vcpus.

When a vcore starts to run, it executes in the context of one of the
vcpu threads.  The other vcpu threads all go to sleep and stay asleep
until something happens requiring the vcpu thread to return to qemu,
or to wake up to run the vcore (this can happen when another vcpu
thread goes from busy in host state to blocked).

It can happen that a vcpu goes from blocked to runnable state (e.g.
because of an interrupt), and the vcore it belongs to is already
running.  In that case it can start to run immediately as long as
the none of the vcpus in the vcore have started to exit the guest.
We send the next free thread in the vcore an IPI to get it to start
to execute the guest.  It synchronizes with the other threads via
the vcore->entry_exit_count field to make sure that it doesn't go
into the guest if the other vcpus are exiting by the time that it
is ready to actually enter the guest.

Note that there is no fixed relationship between the hardware thread
number and the vcpu number.  Hardware threads are assigned to vcpus
as they become runnable, so we will always use the lower-numbered
hardware threads in preference to higher-numbered threads if not all
the vcpus in the vcore are runnable, regardless of which vcpus are
runnable.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

1 files changed, 162 insertions, 6 deletions

diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index e6adaadcdff2..c9bf177b7cf2 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -30,8 +30,6 @@
  *                                                                           *
  ****************************************************************************/
 
-#define SHADOW_VCPU_OFF		PACA_KVM_SVCPU
-
 	.globl	kvmppc_skip_interrupt
 kvmppc_skip_interrupt:
 	mfspr	r13,SPRN_SRR0
@@ -79,6 +77,32 @@ _GLOBAL(kvmppc_hv_entry_trampoline)
  *                                                                            *
  *****************************************************************************/
 
+#define XICS_XIRR		4
+#define XICS_QIRR		0xc
+
+/*
+ * We come in here when wakened from nap mode on a secondary hw thread.
+ * Relocation is off and most register values are lost.
+ * r13 points to the PACA.
+ */
+	.globl	kvm_start_guest
+kvm_start_guest:
+	ld	r1,PACAEMERGSP(r13)
+	subi	r1,r1,STACK_FRAME_OVERHEAD
+
+	/* get vcpu pointer */
+	ld	r4, HSTATE_KVM_VCPU(r13)
+
+	/* We got here with an IPI; clear it */
+	ld	r5, HSTATE_XICS_PHYS(r13)
+	li	r0, 0xff
+	li	r6, XICS_QIRR
+	li	r7, XICS_XIRR
+	lwzcix	r8, r5, r7		/* ack the interrupt */
+	sync
+	stbcix	r0, r5, r6		/* clear it */
+	stwcix	r8, r5, r7		/* EOI it */
+
 .global kvmppc_hv_entry
 kvmppc_hv_entry:
 
@@ -200,7 +224,20 @@ kvmppc_hv_entry:
 	slbia
 	ptesync
 
-	/* Switch to guest partition. */
+	/* Increment entry count iff exit count is zero. */
+	ld	r5,HSTATE_KVM_VCORE(r13)
+	addi	r9,r5,VCORE_ENTRY_EXIT
+21:	lwarx	r3,0,r9
+	cmpwi	r3,0x100		/* any threads starting to exit? */
+	bge	secondary_too_late	/* if so we're too late to the party */
+	addi	r3,r3,1
+	stwcx.	r3,0,r9
+	bne	21b
+
+	/* Primary thread switches to guest partition. */
+	lwz	r6,VCPU_PTID(r4)
+	cmpwi	r6,0
+	bne	20f
 	ld	r9,VCPU_KVM(r4)		/* pointer to struct kvm */
 	ld	r6,KVM_SDR1(r9)
 	lwz	r7,KVM_LPID(r9)
@@ -210,7 +247,15 @@ kvmppc_hv_entry:
 	mtspr	SPRN_SDR1,r6		/* switch to partition page table */
 	mtspr	SPRN_LPID,r7
 	isync
-	ld	r8,VCPU_LPCR(r4)
+	li	r0,1
+	stb	r0,VCORE_IN_GUEST(r5)	/* signal secondaries to continue */
+	b	10f
+
+	/* Secondary threads wait for primary to have done partition switch */
+20:	lbz	r0,VCORE_IN_GUEST(r5)
+	cmpwi	r0,0
+	beq	20b
+10:	ld	r8,VCPU_LPCR(r4)
 	mtspr	SPRN_LPCR,r8
 	isync
 
@@ -225,10 +270,12 @@ kvmppc_hv_entry:
 	 * Invalidate the TLB if we could possibly have stale TLB
 	 * entries for this partition on this core due to the use
 	 * of tlbiel.
+	 * XXX maybe only need this on primary thread?
 	 */
 	ld	r9,VCPU_KVM(r4)		/* pointer to struct kvm */
 	lwz	r5,VCPU_VCPUID(r4)
 	lhz	r6,PACAPACAINDEX(r13)
+	rldimi	r6,r5,0,62		/* XXX map as if threads 1:1 p:v */
 	lhz	r8,VCPU_LAST_CPU(r4)
 	sldi	r7,r6,1			/* see if this is the same vcpu */
 	add	r7,r7,r9		/* as last ran on this pcpu */
@@ -512,8 +559,60 @@ hcall_real_cont:
 	ptesync
 
 hdec_soon:
-	/* Switch back to host partition */
+	/* Increment the threads-exiting-guest count in the 0xff00
+	   bits of vcore->entry_exit_count */
+	lwsync
+	ld	r5,HSTATE_KVM_VCORE(r13)
+	addi	r6,r5,VCORE_ENTRY_EXIT
+41:	lwarx	r3,0,r6
+	addi	r0,r3,0x100
+	stwcx.	r0,0,r6
+	bne	41b
+
+	/*
+	 * At this point we have an interrupt that we have to pass
+	 * up to the kernel or qemu; we can't handle it in real mode.
+	 * Thus we have to do a partition switch, so we have to
+	 * collect the other threads, if we are the first thread
+	 * to take an interrupt.  To do this, we set the HDEC to 0,
+	 * which causes an HDEC interrupt in all threads within 2ns
+	 * because the HDEC register is shared between all 4 threads.
+	 * However, we don't need to bother if this is an HDEC
+	 * interrupt, since the other threads will already be on their
+	 * way here in that case.
+	 */
+	cmpwi	r12,BOOK3S_INTERRUPT_HV_DECREMENTER
+	beq	40f
+	cmpwi	r3,0x100	/* Are we the first here? */
+	bge	40f
+	cmpwi	r3,1
+	ble	40f
+	li	r0,0
+	mtspr	SPRN_HDEC,r0
+40:
+
+	/* Secondary threads wait for primary to do partition switch */
 	ld	r4,VCPU_KVM(r9)		/* pointer to struct kvm */
+	ld	r5,HSTATE_KVM_VCORE(r13)
+	lwz	r3,VCPU_PTID(r9)
+	cmpwi	r3,0
+	beq	15f
+	HMT_LOW
+13:	lbz	r3,VCORE_IN_GUEST(r5)
+	cmpwi	r3,0
+	bne	13b
+	HMT_MEDIUM
+	b	16f
+
+	/* Primary thread waits for all the secondaries to exit guest */
+15:	lwz	r3,VCORE_ENTRY_EXIT(r5)
+	srwi	r0,r3,8
+	clrldi	r3,r3,56
+	cmpw	r3,r0
+	bne	15b
+	isync
+
+	/* Primary thread switches back to host partition */
 	ld	r6,KVM_HOST_SDR1(r4)
 	lwz	r7,KVM_HOST_LPID(r4)
 	li	r8,LPID_RSVD		/* switch to reserved LPID */
@@ -522,10 +621,12 @@ hdec_soon:
 	mtspr	SPRN_SDR1,r6		/* switch to partition page table */
 	mtspr	SPRN_LPID,r7
 	isync
+	li	r0,0
+	stb	r0,VCORE_IN_GUEST(r5)
 	lis	r8,0x7fff		/* MAX_INT@h */
 	mtspr	SPRN_HDEC,r8
 
-	ld	r8,KVM_HOST_LPCR(r4)
+16:	ld	r8,KVM_HOST_LPCR(r4)
 	mtspr	SPRN_LPCR,r8
 	isync
 
@@ -634,6 +735,11 @@ hdec_soon:
 	mr	r3, r9
 	bl	.kvmppc_save_fp
 
+	/* Secondary threads go off to take a nap */
+	lwz	r0,VCPU_PTID(r3)
+	cmpwi	r0,0
+	bne	secondary_nap
+
 	/*
 	 * Reload DEC.  HDEC interrupts were disabled when
 	 * we reloaded the host's LPCR value.
@@ -840,6 +946,56 @@ _GLOBAL(kvmppc_h_set_dabr)
 	li	r3,0
 	blr
 
+secondary_too_late:
+	ld	r5,HSTATE_KVM_VCORE(r13)
+	HMT_LOW
+13:	lbz	r3,VCORE_IN_GUEST(r5)
+	cmpwi	r3,0
+	bne	13b
+	HMT_MEDIUM
+	ld	r11,PACA_SLBSHADOWPTR(r13)
+
+	.rept	SLB_NUM_BOLTED
+	ld	r5,SLBSHADOW_SAVEAREA(r11)
+	ld	r6,SLBSHADOW_SAVEAREA+8(r11)
+	andis.	r7,r5,SLB_ESID_V@h
+	beq	1f
+	slbmte	r6,r5
+1:	addi	r11,r11,16
+	.endr
+	b	50f
+
+secondary_nap:
+	/* Clear any pending IPI */
+50:	ld	r5, HSTATE_XICS_PHYS(r13)
+	li	r0, 0xff
+	li	r6, XICS_QIRR
+	stbcix	r0, r5, r6
+
+	/* increment the nap count and then go to nap mode */
+	ld	r4, HSTATE_KVM_VCORE(r13)
+	addi	r4, r4, VCORE_NAP_COUNT
+	lwsync				/* make previous updates visible */
+51:	lwarx	r3, 0, r4
+	addi	r3, r3, 1
+	stwcx.	r3, 0, r4
+	bne	51b
+	isync
+
+	mfspr	r4, SPRN_LPCR
+	li	r0, LPCR_PECE
+	andc	r4, r4, r0
+	ori	r4, r4, LPCR_PECE0	/* exit nap on interrupt */
+	mtspr	SPRN_LPCR, r4
+	li	r0, 0
+	std	r0, HSTATE_SCRATCH0(r13)
+	ptesync
+	ld	r0, HSTATE_SCRATCH0(r13)
+1:	cmpd	r0, r0
+	bne	1b
+	nap
+	b	.
+
 /*
  * Save away FP, VMX and VSX registers.
  * r3 = vcpu pointer