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Commit b4433a7c authored by Alexander Graf's avatar Alexander Graf Committed by Marcelo Tosatti
Browse files

KVM: PPC: Implement 'skip instruction' mode 



To fetch the last instruction we were interrupted on, we enable DR in early
exit code, where we are still in a very transitional phase between guest
and host state.

Most of the time this seemed to work, but another CPU can easily flush our
TLB and HTAB which makes us go in the Linux page fault handler which totally
breaks because we still use the guest's SLB entries.

To work around that, let's introduce a second KVM guest mode that defines
that whenever we get a trap, we don't call the Linux handler or go into
the KVM exit code, but just jump over the faulting instruction.

That way a potentially bad lwz doesn't trigger any faults and we can later
on interpret the invalid instruction we fetched as "fetch didn't work".

Signed-off-by: default avatarAlexander Graf <agraf@suse.de>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent 7e57cba0

arch/powerpc/include/asm/kvm_asm.h

+6 −0
Original line number Diff line number Diff line
@@ -97,4 +97,10 @@ 
#define RESUME_HOST             RESUME_FLAG_HOST

#define RESUME_HOST_NV          (RESUME_FLAG_HOST|RESUME_FLAG_NV)



#define KVM_GUEST_MODE_NONE	0

#define KVM_GUEST_MODE_GUEST	1

#define KVM_GUEST_MODE_SKIP	2



#define KVM_INST_FETCH_FAILED	-1



#endif /* __POWERPC_KVM_ASM_H__ */

arch/powerpc/kvm/book3s_64_rmhandlers.S

+38 −1
Original line number Diff line number Diff line
@@ -49,7 +49,7 @@ kvmppc_trampoline_\intno: 
	mfcr	r12

	stw	r12, PACA_KVM_SCRATCH1(r13)

	lbz	r12, PACA_KVM_IN_GUEST(r13)

	cmpwi	r12, 0

	cmpwi	r12, KVM_GUEST_MODE_NONE

	bne	..kvmppc_handler_hasmagic_\intno

	/* No KVM guest? Then jump back to the Linux handler! */

	lwz	r12, PACA_KVM_SCRATCH1(r13)
@@ -60,6 +60,11 @@ kvmppc_trampoline_\intno: 


	/* Now we know we're handling a KVM guest */

..kvmppc_handler_hasmagic_\intno:



	/* Should we just skip the faulting instruction? */

	cmpwi	r12, KVM_GUEST_MODE_SKIP

	beq	kvmppc_handler_skip_ins



	/* Let's store which interrupt we're handling */

	li	r12, \intno
@@ -85,6 +90,38 @@ INTERRUPT_TRAMPOLINE BOOK3S_INTERRUPT_PERFMON 
INTERRUPT_TRAMPOLINE	BOOK3S_INTERRUPT_ALTIVEC

INTERRUPT_TRAMPOLINE	BOOK3S_INTERRUPT_VSX



/*

 * Bring us back to the faulting code, but skip the

 * faulting instruction.

 *

 * This is a generic exit path from the interrupt

 * trampolines above.

 *

 * Input Registers:

 *

 * R12               = free

 * R13               = PACA

 * PACA.KVM.SCRATCH0 = guest R12

 * PACA.KVM.SCRATCH1 = guest CR

 * SPRG_SCRATCH0     = guest R13

 *

 */

kvmppc_handler_skip_ins:



	/* Patch the IP to the next instruction */

	mfsrr0	r12

	addi	r12, r12, 4

	mtsrr0	r12



	/* Clean up all state */

	lwz	r12, PACA_KVM_SCRATCH1(r13)

	mtcr	r12

	ld	r12, PACA_KVM_SCRATCH0(r13)

	mfspr	r13, SPRN_SPRG_SCRATCH0



	/* And get back into the code */

	RFI



/*

 * This trampoline brings us back to a real mode handler

 *

arch/powerpc/kvm/book3s_64_slb.S

+11 −5
Original line number Diff line number Diff line
@@ -212,10 +212,6 @@ kvmppc_handler_trampoline_exit: 
	mfdar	r5

	mfdsisr	r6



	/* Unset guest state */

	li	r9, 0

	stb	r9, PACA_KVM_IN_GUEST(r13)



	/*

	 * In order for us to easily get the last instruction,

	 * we got the #vmexit at, we exploit the fact that the
@@ -233,18 +229,28 @@ kvmppc_handler_trampoline_exit: 


ld_last_inst:

	/* Save off the guest instruction we're at */



	/* Set guest mode to 'jump over instruction' so if lwz faults

	 * we'll just continue at the next IP. */

	li	r9, KVM_GUEST_MODE_SKIP

	stb	r9, PACA_KVM_IN_GUEST(r13)



	/*    1) enable paging for data */

	mfmsr	r9

	ori	r11, r9, MSR_DR			/* Enable paging for data */

	mtmsr	r11

	/*    2) fetch the instruction */

	/* XXX implement PACA_KVM_IN_GUEST=2 path to safely jump over this */

	li	r0, KVM_INST_FETCH_FAILED	/* In case lwz faults */

	lwz	r0, 0(r3)

	/*    3) disable paging again */

	mtmsr	r9



no_ld_last_inst:



	/* Unset guest mode */

	li	r9, KVM_GUEST_MODE_NONE

	stb	r9, PACA_KVM_IN_GUEST(r13)



	/* Restore bolted entries from the shadow and fix it along the way */



	/* We don't store anything in entry 0, so we don't need to take care of it */

arch/powerpc/kvm/emulate.c

+4 −0
Original line number Diff line number Diff line
@@ -143,6 +143,10 @@ int kvmppc_emulate_instruction(struct kvm_run *run, struct kvm_vcpu *vcpu) 


	pr_debug(KERN_INFO "Emulating opcode %d / %d\n", get_op(inst), get_xop(inst));



	/* Try again next time */

	if (inst == KVM_INST_FETCH_FAILED)

		return EMULATE_DONE;



	switch (get_op(inst)) {

	case OP_TRAP:

#ifdef CONFIG_PPC64