Subject: Re: [PATCH 4/5 v4] KVM: PPC: Alow kvmppc_get_last_inst() to fail

From: Alexander Graf <[email-masked]>
Date: Thu, 03 Jul 2014 15:44:42 +0200

On 28.06.14 00:49, Mihai Caraman wrote:
> On book3e, guest last instruction is read on the exit path using load
> external pid (lwepx) dedicated instruction. This load operation may fail
> due to TLB eviction and execute-but-not-read entries.
>
> This patch lay down the path for an alternative solution to read the guest
> last instruction, by allowing kvmppc_get_lat_inst() function to fail.
> Architecture specific implmentations of kvmppc_load_last_inst() may read
> last guest instruction and instruct the emulation layer to re-execute the
> guest in case of failure.
>
> Make kvmppc_get_last_inst() definition common between architectures.
>
> Signed-off-by: Mihai Caraman <[email-masked]>
> ---
> v4:
>   - these changes compile on book3s, please validate the functionality and
>     do the necessary adaptations!
>   - common declaration and enum for kvmppc_load_last_inst()
>   - remove kvmppc_read_inst() in a preceding patch
>
> v3:
>   - rework patch description
>   - add common definition for kvmppc_get_last_inst()
>   - check return values in book3s code
>
> v2:
>   - integrated kvmppc_get_last_inst() in book3s code and checked build
>   - addressed cosmetic feedback
>
>   arch/powerpc/include/asm/kvm_book3s.h    | 26 ------------------
>   arch/powerpc/include/asm/kvm_booke.h     |  5 ----
>   arch/powerpc/include/asm/kvm_ppc.h       | 24 +++++++++++++++++
>   arch/powerpc/kvm/book3s.c                | 11 ++++++++
>   arch/powerpc/kvm/book3s_64_mmu_hv.c      | 17 ++++--------
>   arch/powerpc/kvm/book3s_paired_singles.c | 38 +++++++++++++++++----------
>   arch/powerpc/kvm/book3s_pr.c             | 45 ++++++++++++++++++++++++--------
>   arch/powerpc/kvm/booke.c                 |  3 +++
>   arch/powerpc/kvm/e500_mmu_host.c         |  6 +++++
>   arch/powerpc/kvm/emulate.c               | 18 ++++++++-----
>   arch/powerpc/kvm/powerpc.c               | 11 ++++++--
>   11 files changed, 128 insertions(+), 76 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/kvm_book3s.h b/arch/powerpc/include/asm/kvm_book3s.h
> index ceb70aa..1300cd9 100644
> --- a/arch/powerpc/include/asm/kvm_book3s.h
> +++ b/arch/powerpc/include/asm/kvm_book3s.h
> @@ -276,32 +276,6 @@ static inline bool kvmppc_need_byteswap(struct kvm_vcpu *vcpu)
>   	return (kvmppc_get_msr(vcpu) & MSR_LE) != (MSR_KERNEL & MSR_LE);
>   }
>   
> -static inline u32 kvmppc_get_last_inst_internal(struct kvm_vcpu *vcpu, ulong pc)
> -{
> -	/* Load the instruction manually if it failed to do so in the
> -	 * exit path */
> -	if (vcpu->arch.last_inst == KVM_INST_FETCH_FAILED)
> -		kvmppc_ld(vcpu, &pc, sizeof(u32), &vcpu->arch.last_inst, false);
> -
> -	return kvmppc_need_byteswap(vcpu) ? swab32(vcpu->arch.last_inst) :
> -		vcpu->arch.last_inst;
> -}
> -
> -static inline u32 kvmppc_get_last_inst(struct kvm_vcpu *vcpu)
> -{
> -	return kvmppc_get_last_inst_internal(vcpu, kvmppc_get_pc(vcpu));
> -}
> -
> -/*
> - * Like kvmppc_get_last_inst(), but for fetching a sc instruction.
> - * Because the sc instruction sets SRR0 to point to the following
> - * instruction, we have to fetch from pc - 4.
> - */
> -static inline u32 kvmppc_get_last_sc(struct kvm_vcpu *vcpu)
> -{
> -	return kvmppc_get_last_inst_internal(vcpu, kvmppc_get_pc(vcpu) - 4);
> -}
> -
>   static inline ulong kvmppc_get_fault_dar(struct kvm_vcpu *vcpu)
>   {
>   	return vcpu->arch.fault_dar;
> diff --git a/arch/powerpc/include/asm/kvm_booke.h b/arch/powerpc/include/asm/kvm_booke.h
> index c7aed61..cbb1990 100644
> --- a/arch/powerpc/include/asm/kvm_booke.h
> +++ b/arch/powerpc/include/asm/kvm_booke.h
> @@ -69,11 +69,6 @@ static inline bool kvmppc_need_byteswap(struct kvm_vcpu *vcpu)
>   	return false;
>   }
>   
> -static inline u32 kvmppc_get_last_inst(struct kvm_vcpu *vcpu)
> -{
> -	return vcpu->arch.last_inst;
> -}
> -
>   static inline void kvmppc_set_ctr(struct kvm_vcpu *vcpu, ulong val)
>   {
>   	vcpu->arch.ctr = val;
> diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h
> index e2fd5a1..ec326c8 100644
> --- a/arch/powerpc/include/asm/kvm_ppc.h
> +++ b/arch/powerpc/include/asm/kvm_ppc.h
> @@ -47,6 +47,11 @@ enum emulation_result {
>   	EMULATE_EXIT_USER,    /* emulation requires exit to user-space */
>   };
>   
> +enum instruction_type {
> +	INST_GENERIC,
> +	INST_SC,		/* system call */
> +};
> +
>   extern int kvmppc_vcpu_run(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu);
>   extern int __kvmppc_vcpu_run(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu);
>   extern void kvmppc_handler_highmem(void);
> @@ -62,6 +67,9 @@ extern int kvmppc_handle_store(struct kvm_run *run, struct kvm_vcpu *vcpu,
>   			       u64 val, unsigned int bytes,
>   			       int is_default_endian);
>   
> +extern int kvmppc_load_last_inst(struct kvm_vcpu *vcpu,
> +				 enum instruction_type type, u32 *inst);
> +
>   extern int kvmppc_emulate_instruction(struct kvm_run *run,
>                                         struct kvm_vcpu *vcpu);
>   extern int kvmppc_emulate_mmio(struct kvm_run *run, struct kvm_vcpu *vcpu);
> @@ -234,6 +242,22 @@ struct kvmppc_ops {
>   extern struct kvmppc_ops *kvmppc_hv_ops;
>   extern struct kvmppc_ops *kvmppc_pr_ops;
>   
> +static inline int kvmppc_get_last_inst(struct kvm_vcpu *vcpu,
> +					enum instruction_type type, u32 *inst)
> +{
> +	int ret = EMULATE_DONE;
> +
> +	/* Load the instruction manually if it failed to do so in the
> +	 * exit path */
> +	if (vcpu->arch.last_inst == KVM_INST_FETCH_FAILED)
> +		ret = kvmppc_load_last_inst(vcpu, type, &vcpu->arch.last_inst);
> +
> +	*inst = kvmppc_need_byteswap(vcpu) ? swab32(vcpu->arch.last_inst) :
> +		vcpu->arch.last_inst;

We swap needlessly when the translation failed, but I don't think it 
really hurts.

> +
> +	return ret;

So here we just return the return value of kvmppc_load_last_inst() ...

> +}
> +
>   static inline bool is_kvmppc_hv_enabled(struct kvm *kvm)
>   {
>   	return kvm->arch.kvm_ops == kvmppc_hv_ops;
> diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
> index bd75902..c17f101 100644
> --- a/arch/powerpc/kvm/book3s.c
> +++ b/arch/powerpc/kvm/book3s.c
> @@ -467,6 +467,17 @@ mmio:
>   }
>   EXPORT_SYMBOL_GPL(kvmppc_ld);
>   
> +int kvmppc_load_last_inst(struct kvm_vcpu *vcpu, enum instruction_type type,
> +					 u32 *inst)
> +{
> +	ulong pc = kvmppc_get_pc(vcpu);
> +
> +	if (type == INST_SC)
> +		pc -= 4;
> +	return kvmppc_ld(vcpu, &pc, sizeof(u32), &vcpu->arch.last_inst, false);

... which simply returns the return value of kvmppc_ld(). However, 
kvmppc_ld() returns -ENOENT when it doesn't find a translation. We need 
to convert the return value space of kvmppc_ld() into an EMULATE_ name 
space that makes sense for this function.

How about something like

   r = kvmppc_ld();
   if (r == EMULATE_DONE)
     return r;
   else
     return EMULATE_AGAIN;

That way we make sure that we tell the caller only "yes, all is good" or 
"please go back into the guest".

> +}
> +EXPORT_SYMBOL_GPL(kvmppc_load_last_inst);
> +
>   int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu)
>   {
>   	return 0;
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> index 8056107..2c2b7ad 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> @@ -530,21 +530,14 @@ static int instruction_is_store(unsigned int instr)
>   static int kvmppc_hv_emulate_mmio(struct kvm_run *run, struct kvm_vcpu *vcpu,
>   				  unsigned long gpa, gva_t ea, int is_store)
>   {
> -	int ret;
>   	u32 last_inst;
> -	unsigned long srr0 = kvmppc_get_pc(vcpu);
>   
> -	/* We try to load the last instruction.  We don't let
> -	 * emulate_instruction do it as it doesn't check what
> -	 * kvmppc_ld returns.
> +	/*
>   	 * If we fail, we just return to the guest and try executing it again.
>   	 */
> -	if (vcpu->arch.last_inst == KVM_INST_FETCH_FAILED) {
> -		ret = kvmppc_ld(vcpu, &srr0, sizeof(u32), &last_inst, false);
> -		if (ret != EMULATE_DONE || last_inst == KVM_INST_FETCH_FAILED)
> -			return RESUME_GUEST;
> -		vcpu->arch.last_inst = last_inst;
> -	}
> +	if (kvmppc_get_last_inst(vcpu, INST_GENERIC, &last_inst) !=
> +		EMULATE_DONE)
> +		return RESUME_GUEST;

This looks great.

>   
>   	/*
>   	 * WARNING: We do not know for sure whether the instruction we just
> @@ -558,7 +551,7 @@ static int kvmppc_hv_emulate_mmio(struct kvm_run *run, struct kvm_vcpu *vcpu,
>   	 * we just return and retry the instruction.
>   	 */
>   
> -	if (instruction_is_store(kvmppc_get_last_inst(vcpu)) != !!is_store)
> +	if (instruction_is_store(last_inst) != !!is_store)
>   		return RESUME_GUEST;
>   
>   	/*
> diff --git a/arch/powerpc/kvm/book3s_paired_singles.c b/arch/powerpc/kvm/book3s_paired_singles.c
> index 6c8011f..bfb8035 100644
> --- a/arch/powerpc/kvm/book3s_paired_singles.c
> +++ b/arch/powerpc/kvm/book3s_paired_singles.c
> @@ -639,26 +639,36 @@ static int kvmppc_ps_one_in(struct kvm_vcpu *vcpu, bool rc,
>   
>   int kvmppc_emulate_paired_single(struct kvm_run *run, struct kvm_vcpu *vcpu)
>   {
> -	u32 inst = kvmppc_get_last_inst(vcpu);
> +	u32 inst;
>   	enum emulation_result emulated = EMULATE_DONE;
> +	int ax_rd, ax_ra, ax_rb, ax_rc;
> +	short full_d;
> +	u64 *fpr_d, *fpr_a, *fpr_b, *fpr_c;
>   
> -	int ax_rd = inst_get_field(inst, 6, 10);
> -	int ax_ra = inst_get_field(inst, 11, 15);
> -	int ax_rb = inst_get_field(inst, 16, 20);
> -	int ax_rc = inst_get_field(inst, 21, 25);
> -	short full_d = inst_get_field(inst, 16, 31);
> -
> -	u64 *fpr_d = &VCPU_FPR(vcpu, ax_rd);
> -	u64 *fpr_a = &VCPU_FPR(vcpu, ax_ra);
> -	u64 *fpr_b = &VCPU_FPR(vcpu, ax_rb);
> -	u64 *fpr_c = &VCPU_FPR(vcpu, ax_rc);
> -
> -	bool rcomp = (inst & 1) ? true : false;
> -	u32 cr = kvmppc_get_cr(vcpu);
> +	bool rcomp;
> +	u32 cr;
>   #ifdef DEBUG
>   	int i;
>   #endif
>   
> +	emulated = kvmppc_get_last_inst(vcpu, INST_GENERIC, &inst);
> +	if (emulated != EMULATE_DONE)
> +		return emulated;

Here we're already leaking the "emulated" return value into the caller. 
The caller in this chain should know what EMULATE_AGAIN means, so with 
the change above we're safe.

> +
> +	ax_rd = inst_get_field(inst, 6, 10);
> +	ax_ra = inst_get_field(inst, 11, 15);
> +	ax_rb = inst_get_field(inst, 16, 20);
> +	ax_rc = inst_get_field(inst, 21, 25);
> +	full_d = inst_get_field(inst, 16, 31);
> +
> +	fpr_d = &VCPU_FPR(vcpu, ax_rd);
> +	fpr_a = &VCPU_FPR(vcpu, ax_ra);
> +	fpr_b = &VCPU_FPR(vcpu, ax_rb);
> +	fpr_c = &VCPU_FPR(vcpu, ax_rc);
> +
> +	rcomp = (inst & 1) ? true : false;
> +	cr = kvmppc_get_cr(vcpu);
> +
>   	if (!kvmppc_inst_is_paired_single(vcpu, inst))
>   		return EMULATE_FAIL;
>   
> diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
> index d247d88..7bbaeec 100644
> --- a/arch/powerpc/kvm/book3s_pr.c
> +++ b/arch/powerpc/kvm/book3s_pr.c
> @@ -970,15 +970,24 @@ int kvmppc_handle_exit_pr(struct kvm_run *run, struct kvm_vcpu *vcpu,
>   	{
>   		enum emulation_result er;
>   		ulong flags;
> +		u32 last_inst;
> +		int emul;
>   
>   program_interrupt:
>   		flags = vcpu->arch.shadow_srr1 & 0x1f0000ull;
>   
> +		emul = kvmppc_get_last_inst(vcpu, INST_GENERIC, &last_inst);
> +		if (emul != EMULATE_DONE) {
> +			r = RESUME_GUEST;

Yes, this looks good.

> +			break;
> +		}
> +
>   		if (kvmppc_get_msr(vcpu) & MSR_PR) {
>   #ifdef EXIT_DEBUG
> -			printk(KERN_INFO "Userspace triggered 0x700 exception at 0x%lx (0x%x)\n", kvmppc_get_pc(vcpu), kvmppc_get_last_inst(vcpu));
> +			pr_info("Userspace triggered 0x700 exception at\n 0x%lx (0x%x)\n",
> +				kvmppc_get_pc(vcpu), last_inst);
>   #endif
> -			if ((kvmppc_get_last_inst(vcpu) & 0xff0007ff) !=
> +			if ((last_inst & 0xff0007ff) !=
>   			    (INS_DCBZ & 0xfffffff7)) {
>   				kvmppc_core_queue_program(vcpu, flags);
>   				r = RESUME_GUEST;
> @@ -997,7 +1006,7 @@ program_interrupt:
>   			break;
>   		case EMULATE_FAIL:
>   			printk(KERN_CRIT "%s: emulation at %lx failed (%08x)\n",
> -			       __func__, kvmppc_get_pc(vcpu), kvmppc_get_last_inst(vcpu));
> +			       __func__, kvmppc_get_pc(vcpu), last_inst);
>   			kvmppc_core_queue_program(vcpu, flags);
>   			r = RESUME_GUEST;
>   			break;
> @@ -1014,8 +1023,25 @@ program_interrupt:
>   		break;
>   	}
>   	case BOOK3S_INTERRUPT_SYSCALL:
> +	{
> +		u32 last_sc;
> +		int emul;
> +
> +		/* Get last sc for papr */
> +		if (vcpu->arch.papr_enabled) {
> +			/*
> +			 * The sc instuction sets SRR0 to point to the next inst
> +			 */
> +			emul = kvmppc_get_last_inst(vcpu, INST_SC, &last_sc);
> +			if (emul != EMULATE_DONE) {
> +				kvmppc_set_pc(vcpu, kvmppc_get_pc(vcpu) - 4);
> +				r = RESUME_GUEST;

This also looks good :).

> +				break;
> +			}
> +		}
> +
>   		if (vcpu->arch.papr_enabled &&
> -		    (kvmppc_get_last_sc(vcpu) == 0x44000022) &&
> +		    (last_sc == 0x44000022) &&
>   		    !(kvmppc_get_msr(vcpu) & MSR_PR)) {
>   			/* SC 1 papr hypercalls */
>   			ulong cmd = kvmppc_get_gpr(vcpu, 3);
> @@ -1060,13 +1086,13 @@ program_interrupt:
>   			r = RESUME_GUEST;
>   		}
>   		break;
> +	}
>   	case BOOK3S_INTERRUPT_FP_UNAVAIL:
>   	case BOOK3S_INTERRUPT_ALTIVEC:
>   	case BOOK3S_INTERRUPT_VSX:
>   	{
>   		int ext_msr = 0;
>   		int emul;
> -		ulong pc;
>   		u32 last_inst;
>   
>   		if (!(vcpu->arch.hflags & BOOK3S_HFLAG_PAIRED_SINGLE)) {
> @@ -1090,9 +1116,7 @@ program_interrupt:
>   			break;
>   		}
>   
> -		pc = kvmppc_get_pc(vcpu);
> -		last_inst = kvmppc_get_last_inst(vcpu);
> -		emul = kvmppc_ld(vcpu, &pc, sizeof(u32), &last_inst, false);
> +		emul = kvmppc_get_last_inst(vcpu, INST_GENERIC, &last_inst);
>   		if (emul == EMULATE_DONE) {
>   			/* we need to emulate this instruction */
>   			goto program_interrupt;
> @@ -1105,9 +1129,8 @@ program_interrupt:
>   	}
>   	case BOOK3S_INTERRUPT_ALIGNMENT:
>   	{
> -		ulong pc = kvmppc_get_pc(vcpu);
> -		u32 last_inst = kvmppc_get_last_inst(vcpu);
> -		int emul = kvmppc_ld(vcpu, &pc, sizeof(u32), &last_inst, false);
> +		u32 last_inst;
> +		int emul = kvmppc_get_last_inst(vcpu, INST_GENERIC, &last_inst);
>   
>   		if (emul == EMULATE_DONE) {
>   			u32 dsisr;
> diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
> index ab62109..34a42b9 100644
> --- a/arch/powerpc/kvm/booke.c
> +++ b/arch/powerpc/kvm/booke.c
> @@ -752,6 +752,9 @@ static int emulation_exit(struct kvm_run *run, struct kvm_vcpu *vcpu)
>   		 * they were actually modified by emulation. */
>   		return RESUME_GUEST_NV;
>   
> +	case EMULATE_AGAIN:
> +		return RESUME_GUEST;

Yup :).

> +
>   	case EMULATE_DO_DCR:
>   		run->exit_reason = KVM_EXIT_DCR;
>   		return RESUME_HOST;
> diff --git a/arch/powerpc/kvm/e500_mmu_host.c b/arch/powerpc/kvm/e500_mmu_host.c
> index dd2cc03..4b4e8d6 100644
> --- a/arch/powerpc/kvm/e500_mmu_host.c
> +++ b/arch/powerpc/kvm/e500_mmu_host.c
> @@ -606,6 +606,12 @@ void kvmppc_mmu_map(struct kvm_vcpu *vcpu, u64 eaddr, gpa_t gpaddr,
>   	}
>   }
>   
> +int kvmppc_load_last_inst(struct kvm_vcpu *vcpu, enum instruction_type type,
> +			  u32 *instr)
> +{
> +	return EMULATE_FAIL;

This should be EMULATE_AGAIN, no?

> +}
> +
>   /************* MMU Notifiers *************/
>   
>   int kvm_unmap_hva(struct kvm *kvm, unsigned long hva)
> diff --git a/arch/powerpc/kvm/emulate.c b/arch/powerpc/kvm/emulate.c
> index da86d9b..c5c64b6 100644
> --- a/arch/powerpc/kvm/emulate.c
> +++ b/arch/powerpc/kvm/emulate.c
> @@ -224,19 +224,25 @@ static int kvmppc_emulate_mfspr(struct kvm_vcpu *vcpu, int sprn, int rt)
>    * from opcode tables in the future. */
>   int kvmppc_emulate_instruction(struct kvm_run *run, struct kvm_vcpu *vcpu)
>   {
> -	u32 inst = kvmppc_get_last_inst(vcpu);
> -	int ra = get_ra(inst);
> -	int rs = get_rs(inst);
> -	int rt = get_rt(inst);
> -	int sprn = get_sprn(inst);
> -	enum emulation_result emulated = EMULATE_DONE;
> +	u32 inst;
> +	int ra, rs, rt, sprn;
> +	enum emulation_result emulated;
>   	int advance = 1;
>   
>   	/* this default type might be overwritten by subcategories */
>   	kvmppc_set_exit_type(vcpu, EMULATED_INST_EXITS);
>   
> +	emulated = kvmppc_get_last_inst(vcpu, false, &inst);
> +	if (emulated != EMULATE_DONE)
> +		return emulated;

and here we're leaking again ;). It's perfectly fine to do so, but let's 
make sure we don't leak -ENOENT :). So here too the fix above should 
make things work.

Alex

> +
>   	pr_debug("Emulating opcode %d / %d\n", get_op(inst), get_xop(inst));
>   
> +	ra = get_ra(inst);
> +	rs = get_rs(inst);
> +	rt = get_rt(inst);
> +	sprn = get_sprn(inst);
> +
>   	switch (get_op(inst)) {
>   	case OP_TRAP:
>   #ifdef CONFIG_PPC_BOOK3S
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 7efc2b7..da54e4b 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -261,6 +261,9 @@ int kvmppc_emulate_mmio(struct kvm_run *run, struct kvm_vcpu *vcpu)
>   		 * actually modified. */
>   		r = RESUME_GUEST_NV;
>   		break;
> +	case EMULATE_AGAIN:
> +		r = RESUME_GUEST;
> +		break;
>   	case EMULATE_DO_MMIO:
>   		run->exit_reason = KVM_EXIT_MMIO;
>   		/* We must reload nonvolatiles because "update" load/store
> @@ -270,11 +273,15 @@ int kvmppc_emulate_mmio(struct kvm_run *run, struct kvm_vcpu *vcpu)
>   		r = RESUME_HOST_NV;
>   		break;
>   	case EMULATE_FAIL:
> +	{
> +		u32 last_inst;
> +
> +		kvmppc_get_last_inst(vcpu, false, &last_inst);
>   		/* XXX Deliver Program interrupt to guest. */
> -		printk(KERN_EMERG "%s: emulation failed (%08x)\n", __func__,
> -		       kvmppc_get_last_inst(vcpu));
> +		pr_emerg("%s: emulation failed (%08x)\n", __func__, last_inst);
>   		r = RESUME_HOST;
>   		break;
> +	}
>   	default:
>   		WARN_ON(1);
>   		r = RESUME_GUEST;