Re: [PATCH v5 14/69] KVM: arm64: nv: Support virtual EL2 exceptions

[Marc Zyngier <maz@kernel.org>]

On Tue, 18 Jan 2022 14:11:09 +0000,
Alexandru Elisei <alexandru.elisei@arm.com> wrote:
> 
> Hi Marc,
> 
> On Mon, Nov 29, 2021 at 08:00:55PM +0000, Marc Zyngier wrote:
> > From: Jintack Lim <jintack.lim@linaro.org>
> > 
> > Support injecting exceptions and performing exception returns to and
> > from virtual EL2.  This must be done entirely in software except when
> > taking an exception from vEL0 to vEL2 when the virtual HCR_EL2.{E2H,TGE}
> > == {1,1}  (a VHE guest hypervisor).
> 
> Might be useful to explain why emulation shouldn't (or can't) be done in
> software in that particular case.
> 
> It looks to me like kvm_inject_nested() and kvm_emulate_nested_eret()
> handles the above case, so why does does it say that emulation must not be
> done entirely in software?

Not quite. What can be done in HW is the transition between EL0 and
vEL2 when the guest is VHE (where EL2 looks just like EL1). Everything
else has to be mediated one way or the other.

> 
> > 
> > Signed-off-by: Jintack Lim <jintack.lim@linaro.org>
> > Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>
> > [maz: switch to common exception injection framework]
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> >  .mailmap                             |   1 +
> >  arch/arm64/include/asm/kvm_arm.h     |  17 +++
> >  arch/arm64/include/asm/kvm_emulate.h |  10 ++
> >  arch/arm64/include/asm/kvm_host.h    |   1 +
> >  arch/arm64/kvm/Makefile              |   2 +-
> >  arch/arm64/kvm/emulate-nested.c      | 176 +++++++++++++++++++++++++++
> >  arch/arm64/kvm/hyp/exception.c       |  49 ++++++--
> >  arch/arm64/kvm/inject_fault.c        |  68 +++++++++--
> >  arch/arm64/kvm/trace_arm.h           |  59 +++++++++
> >  9 files changed, 362 insertions(+), 21 deletions(-)
> >  create mode 100644 arch/arm64/kvm/emulate-nested.c
> > 
> > diff --git a/.mailmap b/.mailmap
> > index 14314e3c5d5e..491238a888cb 100644
> > --- a/.mailmap
> > +++ b/.mailmap
> > @@ -167,6 +167,7 @@ Jeff Layton <jlayton@kernel.org> <jlayton@redhat.com>
> >  Jens Axboe <axboe@suse.de>
> >  Jens Osterkamp <Jens.Osterkamp@de.ibm.com>
> >  Jernej Skrabec <jernej.skrabec@gmail.com> <jernej.skrabec@siol.net>
> > +<jintack@cs.columbia.edu> <jintack.lim@linaro.org>
> >  Jiri Slaby <jirislaby@kernel.org> <jirislaby@gmail.com>
> >  Jiri Slaby <jirislaby@kernel.org> <jslaby@novell.com>
> >  Jiri Slaby <jirislaby@kernel.org> <jslaby@suse.com>
> > diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
> > index a39fcf318c77..589a6b92d741 100644
> > --- a/arch/arm64/include/asm/kvm_arm.h
> > +++ b/arch/arm64/include/asm/kvm_arm.h
> > @@ -359,4 +359,21 @@
> >  #define CPACR_EL1_TTA		(1 << 28)
> >  #define CPACR_EL1_DEFAULT	(CPACR_EL1_FPEN | CPACR_EL1_ZEN_EL1EN)
> >  
> > +#define kvm_mode_names				\
> > +	{ PSR_MODE_EL0t,	"EL0t" },	\
> > +	{ PSR_MODE_EL1t,	"EL1t" },	\
> > +	{ PSR_MODE_EL1h,	"EL1h" },	\
> > +	{ PSR_MODE_EL2t,	"EL2t" },	\
> > +	{ PSR_MODE_EL2h,	"EL2h" },	\
> > +	{ PSR_MODE_EL3t,	"EL3t" },	\
> > +	{ PSR_MODE_EL3h,	"EL3h" },	\
> > +	{ PSR_AA32_MODE_USR,	"32-bit USR" },	\
> > +	{ PSR_AA32_MODE_FIQ,	"32-bit FIQ" },	\
> > +	{ PSR_AA32_MODE_IRQ,	"32-bit IRQ" },	\
> > +	{ PSR_AA32_MODE_SVC,	"32-bit SVC" },	\
> > +	{ PSR_AA32_MODE_ABT,	"32-bit ABT" },	\
> > +	{ PSR_AA32_MODE_HYP,	"32-bit HYP" },	\
> > +	{ PSR_AA32_MODE_UND,	"32-bit UND" },	\
> > +	{ PSR_AA32_MODE_SYS,	"32-bit SYS" }
> > +
> >  #endif /* __ARM64_KVM_ARM_H__ */
> > diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> > index f4b079945d0f..46c849ba281e 100644
> > --- a/arch/arm64/include/asm/kvm_emulate.h
> > +++ b/arch/arm64/include/asm/kvm_emulate.h
> > @@ -33,6 +33,12 @@ enum exception_type {
> >  	except_type_serror	= 0x180,
> >  };
> >  
> > +#define kvm_exception_type_names		\
> > +	{ except_type_sync,	"SYNC"   },	\
> > +	{ except_type_irq,	"IRQ"    },	\
> > +	{ except_type_fiq,	"FIQ"    },	\
> > +	{ except_type_serror,	"SERROR" }
> > +
> >  bool kvm_condition_valid32(const struct kvm_vcpu *vcpu);
> >  void kvm_skip_instr32(struct kvm_vcpu *vcpu);
> >  
> > @@ -41,6 +47,10 @@ void kvm_inject_vabt(struct kvm_vcpu *vcpu);
> >  void kvm_inject_dabt(struct kvm_vcpu *vcpu, unsigned long addr);
> >  void kvm_inject_pabt(struct kvm_vcpu *vcpu, unsigned long addr);
> >  
> > +void kvm_emulate_nested_eret(struct kvm_vcpu *vcpu);
> > +int kvm_inject_nested_sync(struct kvm_vcpu *vcpu, u64 esr_el2);
> > +int kvm_inject_nested_irq(struct kvm_vcpu *vcpu);
> > +
> >  static __always_inline bool vcpu_el1_is_32bit(struct kvm_vcpu *vcpu)
> >  {
> >  	return !(vcpu->arch.hcr_el2 & HCR_RW);
> > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index 4f642a2e9c34..7b6fe18ee450 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -477,6 +477,7 @@ struct kvm_vcpu_arch {
> >  #define KVM_ARM64_EXCEPT_AA64_ELx_SERR	(3 << 9)
> >  #define KVM_ARM64_EXCEPT_AA64_EL1	(0 << 11)
> >  #define KVM_ARM64_EXCEPT_AA64_EL2	(1 << 11)
> > +#define KVM_ARM64_EXCEPT_AA64_EL_MASK	(1 << 11)
> >  
> >  /*
> >   * Overlaps with KVM_ARM64_EXCEPT_MASK on purpose so that it can't be
> > diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
> > index 989bb5dad2c8..1f602526e9a2 100644
> > --- a/arch/arm64/kvm/Makefile
> > +++ b/arch/arm64/kvm/Makefile
> > @@ -16,7 +16,7 @@ kvm-y := $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o $(KVM)/eventfd.o \
> >  	 inject_fault.o va_layout.o handle_exit.o \
> >  	 guest.o debug.o reset.o sys_regs.o \
> >  	 vgic-sys-reg-v3.o fpsimd.o pmu.o \
> > -	 arch_timer.o trng.o\
> > +	 arch_timer.o trng.o emulate-nested.o \
> >  	 vgic/vgic.o vgic/vgic-init.o \
> >  	 vgic/vgic-irqfd.o vgic/vgic-v2.o \
> >  	 vgic/vgic-v3.o vgic/vgic-v4.o \
> > diff --git a/arch/arm64/kvm/emulate-nested.c b/arch/arm64/kvm/emulate-nested.c
> > new file mode 100644
> > index 000000000000..339e8272b01e
> > --- /dev/null
> > +++ b/arch/arm64/kvm/emulate-nested.c
> > @@ -0,0 +1,176 @@
> > +/*
> > + * Copyright (C) 2016 - Linaro and Columbia University
> > + * Author: Jintack Lim <jintack.lim@linaro.org>
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU General Public License
> > + * along with this program.  If not, see <http://www.gnu.org/licenses/>.
> 
> Wouldn't an SPDX license identifier be better here?

Yup, done.

> 
> > + */
> > +
> > +#include <linux/kvm.h>
> > +#include <linux/kvm_host.h>
> > +
> > +#include <asm/kvm_emulate.h>
> > +#include <asm/kvm_nested.h>
> > +
> > +#include "hyp/include/hyp/adjust_pc.h"
> > +
> > +#include "trace.h"
> > +
> > +void kvm_emulate_nested_eret(struct kvm_vcpu *vcpu)
> > +{
> > +	u64 spsr, elr, mode;
> > +	bool direct_eret;
> > +
> > +	/*
> > +	 * Going through the whole put/load motions is a waste of time
> > +	 * if this is a VHE guest hypervisor returning to its own
> > +	 * userspace, or the hypervisor performing a local exception
> > +	 * return. No need to save/restore registers, no need to
> > +	 * switch S2 MMU. Just do the canonical ERET.
> > +	 */
> > +	spsr = vcpu_read_sys_reg(vcpu, SPSR_EL2);
> > +	mode = spsr & (PSR_MODE_MASK | PSR_MODE32_BIT);
> > +
> > +	direct_eret  = (mode == PSR_MODE_EL0t &&
> > +			vcpu_el2_e2h_is_set(vcpu) &&
> > +			vcpu_el2_tge_is_set(vcpu));
> > +	direct_eret |= (mode == PSR_MODE_EL2h || mode == PSR_MODE_EL2t);
> > +
> > +	if (direct_eret) {
> > +		*vcpu_pc(vcpu) = vcpu_read_sys_reg(vcpu, ELR_EL2);
> > +		*vcpu_cpsr(vcpu) = spsr;
> > +		trace_kvm_nested_eret(vcpu, *vcpu_pc(vcpu), spsr);
> > +		return;
> > +	}
> > +
> > +	preempt_disable();
> > +	kvm_arch_vcpu_put(vcpu);
> > +
> > +	elr = __vcpu_sys_reg(vcpu, ELR_EL2);
> > +
> > +	trace_kvm_nested_eret(vcpu, elr, spsr);
> > +
> > +	/*
> > +	 * Note that the current exception level is always the virtual EL2,
> > +	 * since we set HCR_EL2.NV bit only when entering the virtual EL2.
> > +	 */
> > +	*vcpu_pc(vcpu) = elr;
> > +	*vcpu_cpsr(vcpu) = spsr;
> > +
> > +	kvm_arch_vcpu_load(vcpu, smp_processor_id());
> > +	preempt_enable();
> > +}
> > +
> > +static void kvm_inject_el2_exception(struct kvm_vcpu *vcpu, u64 esr_el2,
> > +				     enum exception_type type)
> > +{
> > +	trace_kvm_inject_nested_exception(vcpu, esr_el2, type);
> > +
> > +	switch (type) {
> > +	case except_type_sync:
> > +		vcpu->arch.flags |= KVM_ARM64_EXCEPT_AA64_ELx_SYNC;
> > +		break;
> > +	case except_type_irq:
> > +		vcpu->arch.flags |= KVM_ARM64_EXCEPT_AA64_ELx_IRQ;
> > +		break;
> > +	default:
> > +		WARN_ONCE(1, "Unsupported EL2 exception injection %d\n", type);
> > +	}
> > +
> > +	vcpu->arch.flags |= (KVM_ARM64_EXCEPT_AA64_EL2		|
> > +			     KVM_ARM64_PENDING_EXCEPTION);
> > +
> > +	vcpu_write_sys_reg(vcpu, esr_el2, ESR_EL2);
> > +}
> > +
> > +/*
> > + * Emulate taking an exception to EL2.
> > + * See ARM ARM J8.1.2 AArch64.TakeException()
> > + */
> > +static int kvm_inject_nested(struct kvm_vcpu *vcpu, u64 esr_el2,
> > +			     enum exception_type type)
> > +{
> > +	u64 pstate, mode;
> > +	bool direct_inject;
> > +
> > +	if (!nested_virt_in_use(vcpu)) {
> > +		kvm_err("Unexpected call to %s for the non-nesting configuration\n",
> > +				__func__);
> > +		return -EINVAL;
> > +	}
> > +
> > +	/*
> > +	 * As for ERET, we can avoid doing too much on the injection path by
> > +	 * checking that we either took the exception from a VHE host
> > +	 * userspace or from vEL2. In these cases, there is no change in
> > +	 * translation regime (or anything else), so let's do as little as
> > +	 * possible.
> > +	 */
> > +	pstate = *vcpu_cpsr(vcpu);
> > +	mode = pstate & (PSR_MODE_MASK | PSR_MODE32_BIT);
> > +
> > +	direct_inject  = (mode == PSR_MODE_EL0t &&
> > +			  vcpu_el2_e2h_is_set(vcpu) &&
> > +			  vcpu_el2_tge_is_set(vcpu));
> > +	direct_inject |= (mode == PSR_MODE_EL2h || mode == PSR_MODE_EL2t);
> > +
> > +	if (direct_inject) {
> > +		kvm_inject_el2_exception(vcpu, esr_el2, type);
> > +		return 1;
> > +	}
> > +
> > +	preempt_disable();
> > +	kvm_arch_vcpu_put(vcpu);
> > +
> > +	kvm_inject_el2_exception(vcpu, esr_el2, type);
> > +
> > +	/*
> > +	 * A hard requirement is that a switch between EL1 and EL2
> > +	 * contexts has to happen between a put/load, so that we can
> > +	 * pick the correct timer and interrupt configuration, among
> > +	 * other things.
> > +	 *
> > +	 * Make sure the exception actually took place before we load
> > +	 * the new context.
> > +	 */
> > +	__kvm_adjust_pc(vcpu);
> > +
> > +	kvm_arch_vcpu_load(vcpu, smp_processor_id());
> > +	preempt_enable();
> > +
> > +	return 1;
> > +}
> > +
> > +int kvm_inject_nested_sync(struct kvm_vcpu *vcpu, u64 esr_el2)
> > +{
> > +	return kvm_inject_nested(vcpu, esr_el2, except_type_sync);
> > +}
> > +
> > +int kvm_inject_nested_irq(struct kvm_vcpu *vcpu)
> 
> I assume this is actually injecting an IRQ to the guest's virtual EL2, not
> a nested interrupt, right?

Neither, really. This is injecting an IRQ *exception* into the guest.
The actual interrupt delivery is done via the vgic. If nested
interrupts (in the interrupt preemption sense) have to happen, the
vgic will take care of it.

> 
> > +{
> > +	/*
> > +	 * Do not inject an irq if the:
> > +	 *  - Current exception level is EL2, and
> > +	 *  - virtual HCR_EL2.TGE == 0
> > +	 *  - virtual HCR_EL2.IMO == 0
> > +	 *
> > +	 * See Table D1-17 "Physical interrupt target and masking when EL3 is
> > +	 * not implemented and EL2 is implemented" in ARM DDI 0487C.a.
> 
> That's now Table D1-13 in ARM DDI 0487G.a, the latest Arm ARM as of now, in
> case you want to update the comment. The table name isn't unchanged, so
> that can be used to find it in newer versions, so I don't think the update
> is strictly necessary.
> 
> I assume the comment refers to the first line of the table, as that's the
> only case when an interrupt is unconditionally not taken when asserted.
> But according to the table, the interrupt is not taken when the *target* EL
> is EL1 and the CPU is executing at EL2. Which makes me very confused. Isn't
> this function supposed to inject an interrupt to virtual EL2? If this
> function also injects interrupts to virtual EL1, why doesn't it also check
> that the target EL is EL1 before returning?

This is already checked by the caller: see kvm_vgic_flush_hwstate()
which has the following sequence:

	if (vgic_state_is_nested(vcpu)) {
		if (kvm_vgic_vcpu_pending_irq(vcpu))
			kvm_make_request(KVM_REQ_GUEST_HYP_IRQ_PENDING, vcpu);

which ends up triggering the exception injection.

> 
> > +	 */
> > +
> > +	if (vcpu_mode_el2(vcpu) && !vcpu_el2_tge_is_set(vcpu) &&
> > +	    !(__vcpu_sys_reg(vcpu, HCR_EL2) & HCR_IMO))
> > +		return 1;
> > +
> > +	/* esr_el2 value doesn't matter for exits due to irqs. */
> > +	return kvm_inject_nested(vcpu, 0, except_type_irq);
> > +}
> > diff --git a/arch/arm64/kvm/hyp/exception.c b/arch/arm64/kvm/hyp/exception.c
> > index 0418399e0a20..4ef5e86efd8b 100644
> > --- a/arch/arm64/kvm/hyp/exception.c
> > +++ b/arch/arm64/kvm/hyp/exception.c
> > @@ -13,6 +13,7 @@
> >  #include <hyp/adjust_pc.h>
> >  #include <linux/kvm_host.h>
> >  #include <asm/kvm_emulate.h>
> > +#include <asm/kvm_nested.h>
> >  
> >  #if !defined (__KVM_NVHE_HYPERVISOR__) && !defined (__KVM_VHE_HYPERVISOR__)
> >  #error Hypervisor code only!
> > @@ -22,7 +23,9 @@ static inline u64 __vcpu_read_sys_reg(const struct kvm_vcpu *vcpu, int reg)
> >  {
> >  	u64 val;
> >  
> > -	if (__vcpu_read_sys_reg_from_cpu(reg, &val))
> > +	if (unlikely(nested_virt_in_use(vcpu)))
> > +		return vcpu_read_sys_reg(vcpu, reg);
> > +	else if (__vcpu_read_sys_reg_from_cpu(reg, &val))
> >  		return val;
> 
> I find the above unintuitive. The original code duplicated the
> functionality from sys_regs.c::vcpu_read_sys_reg() in order to be able to
> run the code at EL2 in the protected KVM case. So why are we now adding
> back the dependency to the EL1 code? Yes, the call to vcpu_read_sys_reg()
> is never compiled because of how nested_virt_in_use() is defined, but still
> looks unconsistent with the purpose of the function (and this file).
> 
> After careful digging, I realized why this change is needed:
> kvm_inject_nested() calls __kvm_adjust_pc() after a vcpu_put(), so the
> function needs to check vcpu->arch.sysregs_loaded_on_cpu, which now can be
> false. Why not copy the body of vcpu_read_sys_reg(), which is what
> __vcpu_read_sys_reg is supposed to do? With a comment explaining why
> sysregs_loaded_on_cpu can be false, I think the code would be a lot more
> understandable.
> 
> Or is it that you want all VCPU register accesses to be done with
> vcpu_read_sys_reg() when the VCPU has the EL2 feature?

Both. The whole NV support is based on this "put/load" sequences when
we alternate between EL{0,1} and EL2, and tracking whether you're
loaded or not is really difficult. I agree that this is pretty ugly,
but I also don't want to spread the crap everywhere (and I have
trouble keeping both the NV and pKVM models in my head at the same
time!).

> 
> >  
> >  	return __vcpu_sys_reg(vcpu, reg);
> > @@ -30,14 +33,24 @@ static inline u64 __vcpu_read_sys_reg(const struct kvm_vcpu *vcpu, int reg)
> >  
> >  static inline void __vcpu_write_sys_reg(struct kvm_vcpu *vcpu, u64 val, int reg)
> >  {
> > -	if (__vcpu_write_sys_reg_to_cpu(val, reg))
> > -		return;
> > -
> > -	 __vcpu_sys_reg(vcpu, reg) = val;
> > +	if (unlikely(nested_virt_in_use(vcpu)))
> > +		vcpu_write_sys_reg(vcpu, val, reg);
> > +	else if (!__vcpu_write_sys_reg_to_cpu(val, reg))
> > +		__vcpu_sys_reg(vcpu, reg) = val;
> >  }
> >  
> > -static void __vcpu_write_spsr(struct kvm_vcpu *vcpu, u64 val)
> > +static void __vcpu_write_spsr(struct kvm_vcpu *vcpu, unsigned long target_mode,
> > +			      u64 val)
> >  {
> > +	if (unlikely(nested_virt_in_use(vcpu))) {
> > +		if (target_mode == PSR_MODE_EL1h)
> > +			vcpu_write_sys_reg(vcpu, val, SPSR_EL1);
> > +		else
> > +			vcpu_write_sys_reg(vcpu, val, SPSR_EL2);
> > +
> > +		return;
> > +	}
> > +
> >  	write_sysreg_el1(val, SYS_SPSR);
> >  }
> >  
> > @@ -97,6 +110,11 @@ static void enter_exception64(struct kvm_vcpu *vcpu, unsigned long target_mode,
> >  		sctlr = __vcpu_read_sys_reg(vcpu, SCTLR_EL1);
> >  		__vcpu_write_sys_reg(vcpu, *vcpu_pc(vcpu), ELR_EL1);
> >  		break;
> > +	case PSR_MODE_EL2h:
> > +		vbar = __vcpu_read_sys_reg(vcpu, VBAR_EL2);
> > +		sctlr = __vcpu_read_sys_reg(vcpu, SCTLR_EL2);
> > +		__vcpu_write_sys_reg(vcpu, *vcpu_pc(vcpu), ELR_EL2);
> > +		break;
> >  	default:
> >  		/* Don't do that */
> >  		BUG();
> > @@ -149,7 +167,7 @@ static void enter_exception64(struct kvm_vcpu *vcpu, unsigned long target_mode,
> >  	new |= target_mode;
> >  
> >  	*vcpu_cpsr(vcpu) = new;
> > -	__vcpu_write_spsr(vcpu, old);
> > +	__vcpu_write_spsr(vcpu, target_mode, old);
> >  }
> >  
> >  /*
> > @@ -320,11 +338,22 @@ static void kvm_inject_exception(struct kvm_vcpu *vcpu)
> >  		      KVM_ARM64_EXCEPT_AA64_EL1):
> >  			enter_exception64(vcpu, PSR_MODE_EL1h, except_type_sync);
> >  			break;
> > +
> > +		case (KVM_ARM64_EXCEPT_AA64_ELx_SYNC |
> > +		      KVM_ARM64_EXCEPT_AA64_EL2):
> > +			enter_exception64(vcpu, PSR_MODE_EL2h, except_type_sync);
> > +			break;
> > +
> > +		case (KVM_ARM64_EXCEPT_AA64_ELx_IRQ |
> > +		      KVM_ARM64_EXCEPT_AA64_EL2):
> > +			enter_exception64(vcpu, PSR_MODE_EL2h, except_type_irq);
> > +			break;
> > +
> >  		default:
> >  			/*
> > -			 * Only EL1_SYNC makes sense so far, EL2_{SYNC,IRQ}
> > -			 * will be implemented at some point. Everything
> > -			 * else gets silently ignored.
> > +			 * Only EL1_SYNC and EL2_{SYNC,IRQ} makes
> > +			 * sense so far. Everything else gets silently
> > +			 * ignored.
> >  			 */
> >  			break;
> >  		}
> > diff --git a/arch/arm64/kvm/inject_fault.c b/arch/arm64/kvm/inject_fault.c
> > index b47df73e98d7..5dcf3f8b08b8 100644
> > --- a/arch/arm64/kvm/inject_fault.c
> > +++ b/arch/arm64/kvm/inject_fault.c
> > @@ -12,19 +12,58 @@
> >  
> >  #include <linux/kvm_host.h>
> >  #include <asm/kvm_emulate.h>
> > +#include <asm/kvm_nested.h>
> >  #include <asm/esr.h>
> >  
> > +static void pend_sync_exception(struct kvm_vcpu *vcpu)
> > +{
> > +	vcpu->arch.flags |= (KVM_ARM64_EXCEPT_AA64_ELx_SYNC	|
> > +			     KVM_ARM64_PENDING_EXCEPTION);
> > +
> > +	/* If not nesting, EL1 is the only possible exception target */
> > +	if (likely(!nested_virt_in_use(vcpu))) {
> > +		vcpu->arch.flags |= KVM_ARM64_EXCEPT_AA64_EL1;
> > +		return;
> > +	}
> > +
> > +	/*
> > +	 * With NV, we need to pick between EL1 and EL2. Note that we
> > +	 * never deal with a nesting exception here, hence never
> 
> I don't understand what "a nesting exception" refers to. In
> emulate_nested.c, the comment for kvm_inject_nested() says that it
> emulates taking an exception to EL2, so I assume a *nested*
> exception is an exception injected to guest virtual EL2. But what is
> a *nesting* exception? Am I misunderstanding something?

Same thing. It is just that the code and the comments have been
written by 3 different people, none of whom being native English
speakers, and this is bound to be inconsistent.

Just get over it. ;-)

> 
> > +	 * changing context, and the exception itself can be delayed
> > +	 * until the next entry.
> > +	 */
> > +	switch(*vcpu_cpsr(vcpu) & PSR_MODE_MASK) {
> > +	case PSR_MODE_EL2h:
> > +	case PSR_MODE_EL2t:
> > +		vcpu->arch.flags |= KVM_ARM64_EXCEPT_AA64_EL2;
> > +		break;
> > +	case PSR_MODE_EL1h:
> > +	case PSR_MODE_EL1t:
> > +		vcpu->arch.flags |= KVM_ARM64_EXCEPT_AA64_EL1;
> > +		break;
> > +	case PSR_MODE_EL0t:
> > +		if (vcpu_el2_tge_is_set(vcpu) & HCR_TGE)
> 
> Doesn't vcpu_el2_tge_is_set() already return true if HCR_TGE is set?

Weee!!! Nice catch! Good thing we almost never inject any of those (we
mostly run wel;l behaved SW), as we'd target the wrong exception
level...

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.