[PATCH 0/2] Deal with shadow interrupts after emulated instructions

[PATCH 0/2] Deal with shadow interrupts after emulated instructions

[Glauber Costa]

Same as before, addressing avi's comments

[PATCH 1/2] replace drop_interrupt_shadow by set_interrupt_shadow

[Glauber Costa]

This patch replaces drop_interrupt_shadow with the more
general set_interrupt_shadow, that can either drop or raise
it, depending on its parameter.

Signed-off-by: Glauber Costa <glommer@redhat.com>
CC: H. Peter Anvin <hpa@zytor.com>
CC: Avi Kivity <avi@redhat.com>
CC: Gleb Natapov <gleb@redhat.com>
---
 arch/x86/include/asm/kvm_host.h        |    3 +-
 arch/x86/include/asm/kvm_x86_emulate.h |    3 ++
 arch/x86/kvm/svm.c                     |   32 +++++++++++++++-----
 arch/x86/kvm/vmx.c                     |   49 +++++++++++++++++++++----------
 arch/x86/kvm/x86.c                     |    2 +-
 5 files changed, 63 insertions(+), 26 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 8e680c3..3d933cf 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -510,6 +510,8 @@ struct kvm_x86_ops {
 	void (*run)(struct kvm_vcpu *vcpu, struct kvm_run *run);
 	int (*handle_exit)(struct kvm_run *run, struct kvm_vcpu *vcpu);
 	void (*skip_emulated_instruction)(struct kvm_vcpu *vcpu);
+	void (*set_interrupt_shadow)(struct kvm_vcpu *vcpu, int mask);
+	u32 (*get_interrupt_shadow)(struct kvm_vcpu *vcpu, int mask);
 	void (*patch_hypercall)(struct kvm_vcpu *vcpu,
 				unsigned char *hypercall_addr);
 	void (*set_irq)(struct kvm_vcpu *vcpu, int vec);
@@ -521,7 +523,6 @@ struct kvm_x86_ops {
 	void (*enable_nmi_window)(struct kvm_vcpu *vcpu);
 	void (*enable_irq_window)(struct kvm_vcpu *vcpu);
 	void (*update_cr8_intercept)(struct kvm_vcpu *vcpu, int tpr, int irr);
-	void (*drop_interrupt_shadow)(struct kvm_vcpu *vcpu);
 	int (*set_tss_addr)(struct kvm *kvm, unsigned int addr);
 	int (*get_tdp_level)(void);
 	u64 (*get_mt_mask)(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio);
diff --git a/arch/x86/include/asm/kvm_x86_emulate.h b/arch/x86/include/asm/kvm_x86_emulate.h
index 6a15973..be40d6e 100644
--- a/arch/x86/include/asm/kvm_x86_emulate.h
+++ b/arch/x86/include/asm/kvm_x86_emulate.h
@@ -143,6 +143,9 @@ struct decode_cache {
 	struct fetch_cache fetch;
 };
 
+#define X86_SHADOW_INT_MOV_SS  1
+#define X86_SHADOW_INT_STI     2
+
 struct x86_emulate_ctxt {
 	/* Register state before/after emulation. */
 	struct kvm_vcpu *vcpu;
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index ef43a18..ae29a95 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -202,6 +202,27 @@ static int is_external_interrupt(u32 info)
 	return info == (SVM_EVTINJ_VALID | SVM_EVTINJ_TYPE_INTR);
 }
 
+static u32 svm_get_interrupt_shadow(struct kvm_vcpu *vcpu, int mask)
+{
+	struct vcpu_svm *svm = to_svm(vcpu);
+	u32 ret = 0;
+
+	if (svm->vmcb->control.int_state & SVM_INTERRUPT_SHADOW_MASK)
+		ret |= X86_SHADOW_INT_STI && X86_SHADOW_INT_MOV_SS;
+	return ret & mask;
+}
+
+static void svm_set_interrupt_shadow(struct kvm_vcpu *vcpu, int mask)
+{
+	struct vcpu_svm *svm = to_svm(vcpu);
+
+	if (mask == 0)
+		svm->vmcb->control.int_state &= ~SVM_INTERRUPT_SHADOW_MASK;
+	else
+		svm->vmcb->control.int_state |= SVM_INTERRUPT_SHADOW_MASK;
+
+}
+
 static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
@@ -215,7 +236,7 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
 		       __func__, kvm_rip_read(vcpu), svm->next_rip);
 
 	kvm_rip_write(vcpu, svm->next_rip);
-	svm->vmcb->control.int_state &= ~SVM_INTERRUPT_SHADOW_MASK;
+	svm_set_interrupt_shadow(vcpu, 0);
 }
 
 static int has_svm(void)
@@ -2229,12 +2250,6 @@ static void pre_svm_run(struct vcpu_svm *svm)
 		new_asid(svm, svm_data);
 }
 
-static void svm_drop_interrupt_shadow(struct kvm_vcpu *vcpu)
-{
-	struct vcpu_svm *svm = to_svm(vcpu);
-	svm->vmcb->control.int_state &= ~SVM_INTERRUPT_SHADOW_MASK;
-}
-
 static void svm_inject_nmi(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
@@ -2637,6 +2652,8 @@ static struct kvm_x86_ops svm_x86_ops = {
 	.run = svm_vcpu_run,
 	.handle_exit = handle_exit,
 	.skip_emulated_instruction = skip_emulated_instruction,
+	.set_interrupt_shadow = svm_set_interrupt_shadow,
+	.get_interrupt_shadow = svm_get_interrupt_shadow,
 	.patch_hypercall = svm_patch_hypercall,
 	.set_irq = svm_set_irq,
 	.set_nmi = svm_inject_nmi,
@@ -2646,7 +2663,6 @@ static struct kvm_x86_ops svm_x86_ops = {
 	.enable_nmi_window = enable_nmi_window,
 	.enable_irq_window = enable_irq_window,
 	.update_cr8_intercept = update_cr8_intercept,
-	.drop_interrupt_shadow = svm_drop_interrupt_shadow,
 
 	.set_tss_addr = svm_set_tss_addr,
 	.get_tdp_level = get_npt_level,
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index e8a5649..c28baf8 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -736,23 +736,45 @@ static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
 	vmcs_writel(GUEST_RFLAGS, rflags);
 }
 
+static u32 vmx_get_interrupt_shadow(struct kvm_vcpu *vcpu, int mask)
+{
+	u32 interruptibility = vmcs_read32(GUEST_INTERRUPTIBILITY_INFO);
+	int ret = 0;
+
+	if (interruptibility & GUEST_INTR_STATE_STI)
+		ret |= X86_SHADOW_INT_STI;
+	if (interruptibility & GUEST_INTR_STATE_MOV_SS)
+		ret |= X86_SHADOW_INT_MOV_SS;
+
+	return ret & mask;
+}
+
+static void vmx_set_interrupt_shadow(struct kvm_vcpu *vcpu, int mask)
+{
+	u32 interruptibility_old = vmcs_read32(GUEST_INTERRUPTIBILITY_INFO);
+	u32 interruptibility = interruptibility_old;
+
+	interruptibility &= ~((GUEST_INTR_STATE_STI | GUEST_INTR_STATE_MOV_SS));
+
+	if (mask & X86_SHADOW_INT_MOV_SS)
+		interruptibility |= GUEST_INTR_STATE_MOV_SS;
+	if (mask & X86_SHADOW_INT_STI)
+		interruptibility |= GUEST_INTR_STATE_STI;
+
+	if ((interruptibility != interruptibility_old))
+		vmcs_write32(GUEST_INTERRUPTIBILITY_INFO, interruptibility);
+}
+
 static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
 {
 	unsigned long rip;
-	u32 interruptibility;
 
 	rip = kvm_rip_read(vcpu);
 	rip += vmcs_read32(VM_EXIT_INSTRUCTION_LEN);
 	kvm_rip_write(vcpu, rip);
 
-	/*
-	 * We emulated an instruction, so temporary interrupt blocking
-	 * should be removed, if set.
-	 */
-	interruptibility = vmcs_read32(GUEST_INTERRUPTIBILITY_INFO);
-	if (interruptibility & 3)
-		vmcs_write32(GUEST_INTERRUPTIBILITY_INFO,
-			     interruptibility & ~3);
+	/* skipping an emulated instruction also counts */
+	vmx_set_interrupt_shadow(vcpu, 0);
 }
 
 static void vmx_queue_exception(struct kvm_vcpu *vcpu, unsigned nr,
@@ -2400,12 +2422,6 @@ out:
 	return ret;
 }
 
-void vmx_drop_interrupt_shadow(struct kvm_vcpu *vcpu)
-{
-	vmcs_clear_bits(GUEST_INTERRUPTIBILITY_INFO,
-			GUEST_INTR_STATE_STI | GUEST_INTR_STATE_MOV_SS);
-}
-
 static void enable_irq_window(struct kvm_vcpu *vcpu)
 {
 	u32 cpu_based_vm_exec_control;
@@ -3649,6 +3665,8 @@ static struct kvm_x86_ops vmx_x86_ops = {
 	.run = vmx_vcpu_run,
 	.handle_exit = vmx_handle_exit,
 	.skip_emulated_instruction = skip_emulated_instruction,
+	.set_interrupt_shadow = vmx_set_interrupt_shadow,
+	.get_interrupt_shadow = vmx_get_interrupt_shadow,
 	.patch_hypercall = vmx_patch_hypercall,
 	.set_irq = vmx_inject_irq,
 	.set_nmi = vmx_inject_nmi,
@@ -3658,7 +3676,6 @@ static struct kvm_x86_ops vmx_x86_ops = {
 	.enable_nmi_window = enable_nmi_window,
 	.enable_irq_window = enable_irq_window,
 	.update_cr8_intercept = update_cr8_intercept,
-	.drop_interrupt_shadow = vmx_drop_interrupt_shadow,
 
 	.set_tss_addr = vmx_set_tss_addr,
 	.get_tdp_level = get_ept_level,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2d7082c..3d8fcc5 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3161,7 +3161,7 @@ static void inject_pending_irq(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 		kvm_run->request_interrupt_window;
 
 	if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
-		kvm_x86_ops->drop_interrupt_shadow(vcpu);
+		kvm_x86_ops->set_interrupt_shadow(vcpu, 0);
 
 	inject_irq(vcpu);
 
-- 
1.5.6.6

[PATCH 2/2] deal with interrupt shadow state for emulated instruction

[Glauber Costa]

we currently unblock shadow interrupt state when we skip an instruction,
but failing to do so when we actually emulate one. This blocks interrupts
in key instruction blocks, in particular sti; hlt; sequences

If the instruction emulated is an sti, we have to block shadow interrupts.
The same goes for mov ss. pop ss also needs it, but we don't currently
emulate it.

Without this patch, I cannot boot gpxe option roms at vmx machines.
This is described at https://bugzilla.redhat.com/show_bug.cgi?id=494469

Signed-off-by: Glauber Costa <glommer@redhat.com>
CC: H. Peter Anvin <hpa@zytor.com>
CC: Avi Kivity <avi@redhat.com>
CC: Gleb Natapov <gleb@redhat.com>
---
 arch/x86/include/asm/kvm_x86_emulate.h |    3 +++
 arch/x86/kvm/x86.c                     |    6 +++++-
 arch/x86/kvm/x86_emulate.c             |   26 +++++++++++++++++++++++++-
 3 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/kvm_x86_emulate.h b/arch/x86/include/asm/kvm_x86_emulate.h
index be40d6e..b7ed2c4 100644
--- a/arch/x86/include/asm/kvm_x86_emulate.h
+++ b/arch/x86/include/asm/kvm_x86_emulate.h
@@ -155,6 +155,9 @@ struct x86_emulate_ctxt {
 	int mode;
 	u32 cs_base;
 
+	/* interruptibility state, as a result of execution of STI or MOV SS */
+	int interruptibility;
+
 	/* decode cache */
 	struct decode_cache decode;
 };
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3d8fcc5..b45baff 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2362,7 +2362,7 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
 			u16 error_code,
 			int emulation_type)
 {
-	int r;
+	int r, shadow_mask;
 	struct decode_cache *c;
 
 	kvm_clear_exception_queue(vcpu);
@@ -2416,6 +2416,10 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
 	}
 
 	r = x86_emulate_insn(&vcpu->arch.emulate_ctxt, &emulate_ops);
+	shadow_mask = vcpu->arch.emulate_ctxt.interruptibility;
+
+	if (r == 0)
+		kvm_x86_ops->set_interrupt_shadow(vcpu, shadow_mask);
 
 	if (vcpu->arch.pio.string)
 		return EMULATE_DO_MMIO;
diff --git a/arch/x86/kvm/x86_emulate.c b/arch/x86/kvm/x86_emulate.c
index d2664fc..b847523 100644
--- a/arch/x86/kvm/x86_emulate.c
+++ b/arch/x86/kvm/x86_emulate.c
@@ -1372,6 +1372,8 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
 	int io_dir_in;
 	int rc = 0;
 
+	ctxt->interruptibility = 0;
+
 	/* Shadow copy of register state. Committed on successful emulation.
 	 * NOTE: we can copy them from vcpu as x86_decode_insn() doesn't
 	 * modify them.
@@ -1618,6 +1620,15 @@ special_insn:
 		int err;
 
 		sel = c->src.val;
+		if (c->modrm_reg == VCPU_SREG_SS) {
+			u32 int_shadow =
+			kvm_x86_ops->get_interrupt_shadow(ctxt->vcpu,
+							  X86_SHADOW_INT_MOV_SS);
+			/* See sti emulation for an explanation of this */
+			if (!(int_shadow & X86_SHADOW_INT_MOV_SS))
+				ctxt->interruptibility = X86_SHADOW_INT_MOV_SS;
+		}
+
 		if (c->modrm_reg <= 5) {
 			type_bits = (c->modrm_reg == 1) ? 9 : 1;
 			err = kvm_load_segment_descriptor(ctxt->vcpu, sel,
@@ -1846,10 +1857,23 @@ special_insn:
 		ctxt->eflags &= ~X86_EFLAGS_IF;
 		c->dst.type = OP_NONE;	/* Disable writeback. */
 		break;
-	case 0xfb: /* sti */
+	case 0xfb: { /* sti */
+		u32 int_shadow =
+		kvm_x86_ops->get_interrupt_shadow(ctxt->vcpu,
+						  X86_SHADOW_INT_STI);
+		/*
+		 * an sti; sti; sequence only disable interrupts for the first
+		 * instruction. So, if the last instruction, be it emulated or
+		 * not, left the system with the INT_STI flag enabled, it
+		 * means that the last instruction is an sti. We should not
+		 * leave the flag on in this case
+		 */
+		if (!(int_shadow & X86_SHADOW_INT_STI))
+			ctxt->interruptibility = X86_SHADOW_INT_STI;
 		ctxt->eflags |= X86_EFLAGS_IF;
 		c->dst.type = OP_NONE;	/* Disable writeback. */
 		break;
+	}
 	case 0xfc: /* cld */
 		ctxt->eflags &= ~EFLG_DF;
 		c->dst.type = OP_NONE;	/* Disable writeback. */
-- 
1.5.6.6

Re: [PATCH 2/2] deal with interrupt shadow state for emulated instruction

[Avi Kivity]

Glauber Costa wrote:
> we currently unblock shadow interrupt state when we skip an instruction,
> but failing to do so when we actually emulate one. This blocks interrupts
> in key instruction blocks, in particular sti; hlt; sequences
>
> If the instruction emulated is an sti, we have to block shadow interrupts.
> The same goes for mov ss. pop ss also needs it, but we don't currently
> emulate it.
>
> Without this patch, I cannot boot gpxe option roms at vmx machines.
> This is described at https://bugzilla.redhat.com/show_bug.cgi?id=494469
>
> @@ -1618,6 +1620,15 @@ special_insn:
>  		int err;
>  
>  		sel = c->src.val;
> +		if (c->modrm_reg == VCPU_SREG_SS) {
> +			u32 int_shadow =
> +			kvm_x86_ops->get_interrupt_shadow(ctxt->vcpu,
> +							  X86_SHADOW_INT_MOV_SS);
> +			/* See sti emulation for an explanation of this */
> +			if (!(int_shadow & X86_SHADOW_INT_MOV_SS))
> +				ctxt->interruptibility = X86_SHADOW_INT_MOV_SS;
> +		}
>   

The indentation of the first statement here is annoying.  Suggest a 
function toggle_interruptibility(ctxt, mask).  Would eliminate the need 
for the comment forward reference as well.


-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

Re: [PATCH 1/2] replace drop_interrupt_shadow by set_interrupt_shadow

[Avi Kivity]

Glauber Costa wrote:
> This patch replaces drop_interrupt_shadow with the more
> general set_interrupt_shadow, that can either drop or raise
> it, depending on its parameter.
>
>  }
>  
> +static u32 svm_get_interrupt_shadow(struct kvm_vcpu *vcpu, int mask)
> +{
> +	struct vcpu_svm *svm = to_svm(vcpu);
> +	u32 ret = 0;
> +
> +	if (svm->vmcb->control.int_state & SVM_INTERRUPT_SHADOW_MASK)
> +		ret |= X86_SHADOW_INT_STI && X86_SHADOW_INT_MOV_SS;
> +	return ret & mask;
> +}
>   

&& -> |.

> +
> +static void vmx_set_interrupt_shadow(struct kvm_vcpu *vcpu, int mask)
> +{
> +	u32 interruptibility_old = vmcs_read32(GUEST_INTERRUPTIBILITY_INFO);
> +	u32 interruptibility = interruptibility_old;
> +
> +	interruptibility &= ~((GUEST_INTR_STATE_STI | GUEST_INTR_STATE_MOV_SS));
>   

May drop one layer of parentheses.



-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

[PATCH 0/2] Deal with shadow interrupts after emulated instructions

[Glauber Costa]

Same story, more avi's comments merged.

Re: [PATCH 0/2] Deal with shadow interrupts after emulated instructions

[Avi Kivity]

Glauber Costa wrote:
> Same story, more avi's comments merged.
>
>
>   

Applied, thanks.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

[PATCH 0/2] Deal with shadow interrupts after emulated instructions

[Glauber Costa]

Hi,

This is the same patch you're all used to by now, but split in two per
Avi request.

Re: [PATCH 0/2] Deal with shadow interrupts after emulated instructions

[Gleb Natapov]

On Fri, May 08, 2009 at 04:23:05PM -0400, Glauber Costa wrote:
> Hi,
> 
> This is the same patch you're all used to by now, but split in two per
> Avi request.
> 
> 
Acked-by: Gleb Natapov <gleb@redhat.com>

--
			Gleb.