[PATCH 1/3] KVM: MTRR: fix memory type handling if MTRR is completely disabled

[PATCH 1/3] KVM: MTRR: fix memory type handling if MTRR is completely disabled

[Xiao Guangrong]

From: Xiao Guangrong <guangrong.xiao@intel.com>

Currently code uses default memory type if MTRR is fully disabled,
fix it by using UC instead

Signed-off-by: Xiao Guangrong <guangrong.xiao@intel.com>
---
 arch/x86/kvm/mtrr.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
index de1d2d8..e275013 100644
--- a/arch/x86/kvm/mtrr.c
+++ b/arch/x86/kvm/mtrr.c
@@ -120,6 +120,16 @@ static u8 mtrr_default_type(struct kvm_mtrr *mtrr_state)
 	return mtrr_state->deftype & IA32_MTRR_DEF_TYPE_TYPE_MASK;
 }
 
+static u8 mtrr_disabled_type(void)
+{
+	/*
+	 * Intel SDM 11.11.2.2: all MTRRs are disabled when
+	 * IA32_MTRR_DEF_TYPE.E bit is cleared, and the UC
+	 * memory type is applied to all of physical memory.
+	 */
+	return MTRR_TYPE_UNCACHABLE;
+}
+
 /*
 * Three terms are used in the following code:
 * - segment, it indicates the address segments covered by fixed MTRRs.
@@ -434,6 +444,8 @@ struct mtrr_iter {
 
 	/* output fields. */
 	int mem_type;
+	/* mtrr is completely disabled? */
+	bool mtrr_disabled;
 	/* [start, end) is not fully covered in MTRRs? */
 	bool partial_map;
 
@@ -549,7 +561,7 @@ static void mtrr_lookup_var_next(struct mtrr_iter *iter)
 static void mtrr_lookup_start(struct mtrr_iter *iter)
 {
 	if (!mtrr_is_enabled(iter->mtrr_state)) {
-		iter->partial_map = true;
+		iter->mtrr_disabled = true;
 		return;
 	}
 
@@ -563,6 +575,7 @@ static void mtrr_lookup_init(struct mtrr_iter *iter,
 	iter->mtrr_state = mtrr_state;
 	iter->start = start;
 	iter->end = end;
+	iter->mtrr_disabled = false;
 	iter->partial_map = false;
 	iter->fixed = false;
 	iter->range = NULL;
@@ -656,6 +669,9 @@ u8 kvm_mtrr_get_guest_memory_type(struct kvm_vcpu *vcpu, gfn_t gfn)
 		return MTRR_TYPE_WRBACK;
 	}
 
+	if (iter.mtrr_disabled)
+		return mtrr_disabled_type();
+
 	/* It is not covered by MTRRs. */
 	if (iter.partial_map) {
 		/*
@@ -689,6 +705,9 @@ bool kvm_mtrr_check_gfn_range_consistency(struct kvm_vcpu *vcpu, gfn_t gfn,
 			return false;
 	}
 
+	if (iter.mtrr_disabled)
+		return true;
+
 	if (!iter.partial_map)
 		return true;
 
-- 
2.1.0

[PATCH 2/3] KVM: MTRR: simplify kvm_mtrr_get_guest_memory_type

[Xiao Guangrong]

From: Xiao Guangrong <guangrong.xiao@intel.com>

kvm_mtrr_get_guest_memory_type never returns -1 which is implied
in the current code since if @type = -1 (means no MTRR contains the
range), iter.partial_map must be true

Simplify the code to indicate this fact

Signed-off-by: Xiao Guangrong <guangrong.xiao@intel.com>
---
 arch/x86/kvm/mtrr.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
index e275013..9e8bf13 100644
--- a/arch/x86/kvm/mtrr.c
+++ b/arch/x86/kvm/mtrr.c
@@ -672,15 +672,16 @@ u8 kvm_mtrr_get_guest_memory_type(struct kvm_vcpu *vcpu, gfn_t gfn)
 	if (iter.mtrr_disabled)
 		return mtrr_disabled_type();
 
-	/* It is not covered by MTRRs. */
-	if (iter.partial_map) {
-		/*
-		 * We just check one page, partially covered by MTRRs is
-		 * impossible.
-		 */
-		WARN_ON(type != -1);
-		type = mtrr_default_type(mtrr_state);
-	}
+	/* not contained in any MTRRs. */
+	if (type == -1)
+		return mtrr_default_type(mtrr_state);
+
+	/*
+	 * We just check one page, partially covered by MTRRs is
+	 * impossible.
+	 */
+	WARN_ON(iter.partial_map);
+
 	return type;
 }
 EXPORT_SYMBOL_GPL(kvm_mtrr_get_guest_memory_type);
-- 
2.1.0

[PATCH 3/3] KVM: x86: quirkily apply WB to all memory if cache is disabled

[Xiao Guangrong]

From: Xiao Guangrong <guangrong.xiao@intel.com>

Current firmware depends on WB to fast boot, please refer to
      https://lkml.org/lkml/2015/7/12/115

Let's us WB if CR0.CD is set to make this kind of firmware happy

This quirk can be dropped by using KVM_ENABLE_CAP API with
KVM_CAP_DISABLE_QUIRKS if the broken firmware is gone

Signed-off-by: Xiao Guangrong <guangrong.xiao@intel.com>
---
 arch/x86/include/uapi/asm/kvm.h | 1 +
 arch/x86/kvm/lapic.c            | 2 +-
 arch/x86/kvm/svm.c              | 2 +-
 arch/x86/kvm/vmx.c              | 5 ++++-
 arch/x86/kvm/x86.c              | 7 +++++++
 arch/x86/kvm/x86.h              | 5 +++++
 6 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index a4ae82e..2f141d4 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -356,5 +356,6 @@ struct kvm_sync_regs {
 
 #define KVM_QUIRK_LINT0_REENABLED	(1 << 0)
 #define KVM_QUIRK_CD_NW_CLEARED		(1 << 1)
+#define KVM_QUIRK_CD_AS_WB		(1 << 2)
 
 #endif /* _ASM_X86_KVM_H */
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 954e98a..0d77b20 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1595,7 +1595,7 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
 	for (i = 0; i < APIC_LVT_NUM; i++)
 		apic_set_reg(apic, APIC_LVTT + 0x10 * i, APIC_LVT_MASKED);
 	apic_update_lvtt(apic);
-	if (!(vcpu->kvm->arch.disabled_quirks & KVM_QUIRK_LINT0_REENABLED))
+	if (!kvm_check_disabled_quirks(vcpu->kvm, KVM_QUIRK_LINT0_REENABLED))
 		apic_set_reg(apic, APIC_LVT0,
 			     SET_APIC_DELIVERY_MODE(0, APIC_MODE_EXTINT));
 	apic_manage_nmi_watchdog(apic, kvm_apic_get_reg(apic, APIC_LVT0));
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index bbc678a..cac9ee6 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1672,7 +1672,7 @@ static void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
 	 * does not do it - this results in some delay at
 	 * reboot
 	 */
-	if (!(vcpu->kvm->arch.disabled_quirks & KVM_QUIRK_CD_NW_CLEARED))
+	if (!kvm_check_disabled_quirks(vcpu->kvm, KVM_QUIRK_CD_NW_CLEARED))
 		cr0 &= ~(X86_CR0_CD | X86_CR0_NW);
 	svm->vmcb->save.cr0 = cr0;
 	mark_dirty(svm->vmcb, VMCB_CR);
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index d342b23..74398db 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -8703,7 +8703,10 @@ static u64 vmx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
 
 	if (kvm_read_cr0(vcpu) & X86_CR0_CD) {
 		ipat = VMX_EPT_IPAT_BIT;
-		cache = MTRR_TYPE_UNCACHABLE;
+		if (kvm_check_disabled_quirks(vcpu->kvm, KVM_QUIRK_CD_AS_WB))
+			cache = MTRR_TYPE_WRBACK;
+		else
+			cache = MTRR_TYPE_UNCACHABLE;
 		goto exit;
 	}
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 28076c2..fd21712 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3575,6 +3575,11 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 	return r;
 }
 
+static void kvm_init_disabled_quirks(struct kvm *kvm)
+{
+	kvm->arch.disabled_quirks = KVM_QUIRK_CD_AS_WB;
+}
+
 long kvm_arch_vm_ioctl(struct file *filp,
 		       unsigned int ioctl, unsigned long arg)
 {
@@ -7422,6 +7427,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	INIT_DELAYED_WORK(&kvm->arch.kvmclock_update_work, kvmclock_update_fn);
 	INIT_DELAYED_WORK(&kvm->arch.kvmclock_sync_work, kvmclock_sync_fn);
 
+	kvm_init_disabled_quirks(kvm);
+
 	return 0;
 }
 
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index c04b56b..ea99928 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -152,6 +152,11 @@ static inline u64 get_kernel_ns(void)
 	return ktime_get_boot_ns();
 }
 
+static inline bool kvm_check_disabled_quirks(struct kvm *kvm, u64 quirk)
+{
+	return !!(kvm->arch.disabled_quirks & quirk);
+}
+
 void kvm_before_handle_nmi(struct kvm_vcpu *vcpu);
 void kvm_after_handle_nmi(struct kvm_vcpu *vcpu);
 void kvm_set_pending_timer(struct kvm_vcpu *vcpu);
-- 
2.1.0

Re: [PATCH 1/3] KVM: MTRR: fix memory type handling if MTRR is completely disabled

[Alex Williamson]

On Thu, 2015-07-16 at 03:25 +0800, Xiao Guangrong wrote:
> From: Xiao Guangrong <guangrong.xiao@intel.com>
> 
> Currently code uses default memory type if MTRR is fully disabled,
> fix it by using UC instead
> 
> Signed-off-by: Xiao Guangrong <guangrong.xiao@intel.com>
> ---

Seems to work for me.  I don't see a 0th patch, but for the series:

Tested-by: Alex Williamson <alex.williamson@redhat.com>

Thanks!

>  arch/x86/kvm/mtrr.c | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
> index de1d2d8..e275013 100644
> --- a/arch/x86/kvm/mtrr.c
> +++ b/arch/x86/kvm/mtrr.c
> @@ -120,6 +120,16 @@ static u8 mtrr_default_type(struct kvm_mtrr *mtrr_state)
>  	return mtrr_state->deftype & IA32_MTRR_DEF_TYPE_TYPE_MASK;
>  }
>  
> +static u8 mtrr_disabled_type(void)
> +{
> +	/*
> +	 * Intel SDM 11.11.2.2: all MTRRs are disabled when
> +	 * IA32_MTRR_DEF_TYPE.E bit is cleared, and the UC
> +	 * memory type is applied to all of physical memory.
> +	 */
> +	return MTRR_TYPE_UNCACHABLE;
> +}
> +
>  /*
>  * Three terms are used in the following code:
>  * - segment, it indicates the address segments covered by fixed MTRRs.
> @@ -434,6 +444,8 @@ struct mtrr_iter {
>  
>  	/* output fields. */
>  	int mem_type;
> +	/* mtrr is completely disabled? */
> +	bool mtrr_disabled;
>  	/* [start, end) is not fully covered in MTRRs? */
>  	bool partial_map;
>  
> @@ -549,7 +561,7 @@ static void mtrr_lookup_var_next(struct mtrr_iter *iter)
>  static void mtrr_lookup_start(struct mtrr_iter *iter)
>  {
>  	if (!mtrr_is_enabled(iter->mtrr_state)) {
> -		iter->partial_map = true;
> +		iter->mtrr_disabled = true;
>  		return;
>  	}
>  
> @@ -563,6 +575,7 @@ static void mtrr_lookup_init(struct mtrr_iter *iter,
>  	iter->mtrr_state = mtrr_state;
>  	iter->start = start;
>  	iter->end = end;
> +	iter->mtrr_disabled = false;
>  	iter->partial_map = false;
>  	iter->fixed = false;
>  	iter->range = NULL;
> @@ -656,6 +669,9 @@ u8 kvm_mtrr_get_guest_memory_type(struct kvm_vcpu *vcpu, gfn_t gfn)
>  		return MTRR_TYPE_WRBACK;
>  	}
>  
> +	if (iter.mtrr_disabled)
> +		return mtrr_disabled_type();
> +
>  	/* It is not covered by MTRRs. */
>  	if (iter.partial_map) {
>  		/*
> @@ -689,6 +705,9 @@ bool kvm_mtrr_check_gfn_range_consistency(struct kvm_vcpu *vcpu, gfn_t gfn,
>  			return false;
>  	}
>  
> +	if (iter.mtrr_disabled)
> +		return true;
> +
>  	if (!iter.partial_map)
>  		return true;
>  

Re: [PATCH 3/3] KVM: x86: quirkily apply WB to all memory if cache is disabled

[Paolo Bonzini]

On 15/07/2015 21:25, Xiao Guangrong wrote:
> From: Xiao Guangrong <guangrong.xiao@intel.com>
> 
> Current firmware depends on WB to fast boot, please refer to
>       https://lkml.org/lkml/2015/7/12/115
> 
> Let's us WB if CR0.CD is set to make this kind of firmware happy
> 
> This quirk can be dropped by using KVM_ENABLE_CAP API with
> KVM_CAP_DISABLE_QUIRKS if the broken firmware is gone
> 
> Signed-off-by: Xiao Guangrong <guangrong.xiao@intel.com>

Your patch is actually *enabling* the quirk if KVM_QUIRK_CD_AS_WB is 
included in the disabled quirks.  I'm squashing in this change:

diff --cc arch/x86/kvm/x86.h
index edc8cdcd786b,ea99928d9d09..000000000000
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@@ -147,9 +147,9 @@@ static inline void kvm_register_writel(
 	return ktime_get_boot_ns();
 }
 
-static inline bool kvm_check_disabled_quirks(struct kvm *kvm, u64 quirk)
+static inline bool kvm_check_has_quirk(struct kvm *kvm, u64 quirk)
 {
-	return !!(kvm->arch.disabled_quirks & quirk);
+	return !(kvm->arch.disabled_quirks & quirk);
 }
 
 void kvm_before_handle_nmi(struct kvm_vcpu *vcpu);
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 0d77b20d628a..1c425443a41a 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1595,7 +1595,7 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
 	for (i = 0; i < APIC_LVT_NUM; i++)
 		apic_set_reg(apic, APIC_LVTT + 0x10 * i, APIC_LVT_MASKED);
 	apic_update_lvtt(apic);
-	if (!kvm_check_disabled_quirks(vcpu->kvm, KVM_QUIRK_LINT0_REENABLED))
+	if (kvm_check_has_quirk(vcpu->kvm, KVM_QUIRK_LINT0_REENABLED))
 		apic_set_reg(apic, APIC_LVT0,
 			     SET_APIC_DELIVERY_MODE(0, APIC_MODE_EXTINT));
 	apic_manage_nmi_watchdog(apic, kvm_apic_get_reg(apic, APIC_LVT0));
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index cac9ee6abea7..8cbec765b08d 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1672,7 +1672,7 @@ static void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
 	 * does not do it - this results in some delay at
 	 * reboot
 	 */
-	if (!kvm_check_disabled_quirks(vcpu->kvm, KVM_QUIRK_CD_NW_CLEARED))
+	if (kvm_check_has_quirk(vcpu->kvm, KVM_QUIRK_CD_NW_CLEARED))
 		cr0 &= ~(X86_CR0_CD | X86_CR0_NW);
 	svm->vmcb->save.cr0 = cr0;
 	mark_dirty(svm->vmcb, VMCB_CR);
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 7247891526ae..6b4890623146 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -8650,7 +8650,7 @@ static u64 vmx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
 
 	if (kvm_read_cr0(vcpu) & X86_CR0_CD) {
 		ipat = VMX_EPT_IPAT_BIT;
-		if (kvm_check_disabled_quirks(vcpu->kvm, KVM_QUIRK_CD_AS_WB))
+		if (kvm_check_has_quirk(vcpu->kvm, KVM_QUIRK_CD_AS_WB))
 			cache = MTRR_TYPE_WRBACK;
 		else
 			cache = MTRR_TYPE_UNCACHABLE;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 549051784955..5ef2560075bf 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3765,11 +3765,6 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 	return r;
 }
 
-static void kvm_init_disabled_quirks(struct kvm *kvm)
-{
-	kvm->arch.disabled_quirks = KVM_QUIRK_CD_AS_WB;
-}
-
 long kvm_arch_vm_ioctl(struct file *filp,
 		       unsigned int ioctl, unsigned long arg)
 {
@@ -7671,8 +7666,6 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	INIT_DELAYED_WORK(&kvm->arch.kvmclock_update_work, kvmclock_update_fn);
 	INIT_DELAYED_WORK(&kvm->arch.kvmclock_sync_work, kvmclock_sync_fn);
 
-	kvm_init_disabled_quirks(kvm);
-
 	return 0;
 }
 

to avoid the double negation and invert the meaning of KVM_QUIRK_CD_AS_WB.

Paolo

Re: [PATCH 3/3] KVM: x86: quirkily apply WB to all memory if cache is disabled

[Xiao Guangrong]

On 07/23/2015 01:56 PM, Paolo Bonzini wrote:
>
>
> On 15/07/2015 21:25, Xiao Guangrong wrote:
>> From: Xiao Guangrong <guangrong.xiao@intel.com>
>>
>> Current firmware depends on WB to fast boot, please refer to
>>        https://lkml.org/lkml/2015/7/12/115
>>
>> Let's us WB if CR0.CD is set to make this kind of firmware happy
>>
>> This quirk can be dropped by using KVM_ENABLE_CAP API with
>> KVM_CAP_DISABLE_QUIRKS if the broken firmware is gone
>>
>> Signed-off-by: Xiao Guangrong <guangrong.xiao@intel.com>
>
> Your patch is actually *enabling* the quirk if KVM_QUIRK_CD_AS_WB is
> included in the disabled quirks.  I'm squashing in this change:

Yep, i misunderstood the meaning of "disabled-quirks", thanks for your
nice adjustment, Paolo!

Re: [PATCH 1/3] KVM: MTRR: fix memory type handling if MTRR is completely disabled

[Paolo Bonzini]

On 16/07/2015 06:10, Alex Williamson wrote:
> On Thu, 2015-07-16 at 03:25 +0800, Xiao Guangrong wrote:
>> > From: Xiao Guangrong <guangrong.xiao@intel.com>
>> > 
>> > Currently code uses default memory type if MTRR is fully disabled,
>> > fix it by using UC instead
>> > 
>> > Signed-off-by: Xiao Guangrong <guangrong.xiao@intel.com>
>> > ---
> Seems to work for me.  I don't see a 0th patch, but for the series:
> 
> Tested-by: Alex Williamson <alex.williamson@redhat.com>

In fact this is the same quirk already implemented for SVM as
KVM_QUIRK_CD_NW_CLEARED, so we can reuse the bit.

Paolo

Re: [PATCH 1/3] KVM: MTRR: fix memory type handling if MTRR is completely disabled

[Xiao Guangrong]

On 07/23/2015 02:21 PM, Paolo Bonzini wrote:
>
>
> On 16/07/2015 06:10, Alex Williamson wrote:
>> On Thu, 2015-07-16 at 03:25 +0800, Xiao Guangrong wrote:
>>>> From: Xiao Guangrong <guangrong.xiao@intel.com>
>>>>
>>>> Currently code uses default memory type if MTRR is fully disabled,
>>>> fix it by using UC instead
>>>>
>>>> Signed-off-by: Xiao Guangrong <guangrong.xiao@intel.com>
>>>> ---
>> Seems to work for me.  I don't see a 0th patch, but for the series:
>>
>> Tested-by: Alex Williamson <alex.williamson@redhat.com>
>
> In fact this is the same quirk already implemented for SVM as
> KVM_QUIRK_CD_NW_CLEARED, so we can reuse the bit.

Sounds good to me. I will drop the new bit and reuse as your suggestion.
And i think we need document this whole staff in API.txt ...

Re: [PATCH 1/3] KVM: MTRR: fix memory type handling if MTRR is completely disabled

[Paolo Bonzini]

On 23/07/2015 08:29, Xiao Guangrong wrote:
>> In fact this is the same quirk already implemented for SVM as
>> KVM_QUIRK_CD_NW_CLEARED, so we can reuse the bit.
> 
> Sounds good to me. I will drop the new bit and reuse as your suggestion.
> And i think we need document this whole staff in API.txt ...

No problem, I've already pushed it to kvm/queue.  I'm running tests now
and will send a pull request to Linus tomorrow if all goes well.

Paolo

Re: [PATCH 2/3] KVM: MTRR: simplify kvm_mtrr_get_guest_memory_type

[Alex Williamson]

Hi Paolo,

Something bad happened to this patch.  This is the version I provided
Tested-by for:

On Thu, 2015-07-16 at 03:25 +0800, Xiao Guangrong wrote:
> From: Xiao Guangrong <guangrong.xiao@intel.com>
> 
> kvm_mtrr_get_guest_memory_type never returns -1 which is implied
> in the current code since if @type = -1 (means no MTRR contains the
> range), iter.partial_map must be true
> 
> Simplify the code to indicate this fact
> 
> Signed-off-by: Xiao Guangrong <guangrong.xiao@intel.com>
> ---
>  arch/x86/kvm/mtrr.c | 19 ++++++++++---------
>  1 file changed, 10 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
> index e275013..9e8bf13 100644
> --- a/arch/x86/kvm/mtrr.c
> +++ b/arch/x86/kvm/mtrr.c
> @@ -672,15 +672,16 @@ u8 kvm_mtrr_get_guest_memory_type(struct kvm_vcpu *vcpu, gfn_t gfn)
>  	if (iter.mtrr_disabled)
>  		return mtrr_disabled_type();
>  
> -	/* It is not covered by MTRRs. */
> -	if (iter.partial_map) {
> -		/*
> -		 * We just check one page, partially covered by MTRRs is
> -		 * impossible.
> -		 */
> -		WARN_ON(type != -1);
> -		type = mtrr_default_type(mtrr_state);
> -	}
> +	/* not contained in any MTRRs. */
> +	if (type == -1)
> +		return mtrr_default_type(mtrr_state);
> +
> +	/*
> +	 * We just check one page, partially covered by MTRRs is
> +	 * impossible.
> +	 */
> +	WARN_ON(iter.partial_map);
> +
>  	return type;
>  }
>  EXPORT_SYMBOL_GPL(kvm_mtrr_get_guest_memory_type);


This is the version that was committed for v4.2-rc4:

commit 3e5d2fdceda172554e681b68c853bf5d08205bbf
Author: Xiao Guangrong <guangrong.xiao@intel.com>
Date:   Thu Jul 16 03:25:55 2015 +0800

    KVM: MTRR: simplify kvm_mtrr_get_guest_memory_type
    
    kvm_mtrr_get_guest_memory_type never returns -1 which is implied
    in the current code since if @type = -1 (means no MTRR contains the
    range), iter.partial_map must be true
    
    Simplify the code to indicate this fact
    
    Signed-off-by: Xiao Guangrong <guangrong.xiao@intel.com>
    Tested-by: Alex Williamson <alex.williamson@redhat.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
index e275013..dc0a84a 100644
--- a/arch/x86/kvm/mtrr.c
+++ b/arch/x86/kvm/mtrr.c
@@ -672,15 +672,16 @@ u8 kvm_mtrr_get_guest_memory_type(struct kvm_vcpu *vcpu, gfn_t gfn)
 	if (iter.mtrr_disabled)
 		return mtrr_disabled_type();
 
-	/* It is not covered by MTRRs. */
-	if (iter.partial_map) {
-		/*
-		 * We just check one page, partially covered by MTRRs is
-		 * impossible.
-		 */
-		WARN_ON(type != -1);
-		type = mtrr_default_type(mtrr_state);
-	}
+	/*
+	 * We just check one page, partially covered by MTRRs is
+	 * impossible.
+	 */
+	WARN_ON(iter.partial_map);
+
+	/* not contained in any MTRRs. */
+	if (type == -1)
+		return mtrr_default_type(mtrr_state);
+
 	return type;
 }
 EXPORT_SYMBOL_GPL(kvm_mtrr_get_guest_memory_type);

The WARN_ON() now comes before the type == -1 test and I hit that at
*very* high frequency when trying to test device assignment.  Restoring
the ordering to what Xiao originally proposed resolves the problem.
Thanks,

Alex

Re: [edk2] [PATCH 2/3] KVM: MTRR: simplify kvm_mtrr_get_guest_memory_type

[Paolo Bonzini]

On 29/07/2015 21:07, Alex Williamson wrote:
> diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
> index e275013..dc0a84a 100644
> --- a/arch/x86/kvm/mtrr.c
> +++ b/arch/x86/kvm/mtrr.c
> @@ -672,15 +672,16 @@ u8 kvm_mtrr_get_guest_memory_type(struct kvm_vcpu *vcpu, gfn_t gfn)
>  	if (iter.mtrr_disabled)
>  		return mtrr_disabled_type();
>  
> -	/* It is not covered by MTRRs. */
> -	if (iter.partial_map) {
> -		/*
> -		 * We just check one page, partially covered by MTRRs is
> -		 * impossible.
> -		 */
> -		WARN_ON(type != -1);
> -		type = mtrr_default_type(mtrr_state);
> -	}
> +	/*
> +	 * We just check one page, partially covered by MTRRs is
> +	 * impossible.
> +	 */
> +	WARN_ON(iter.partial_map);
> +
> +	/* not contained in any MTRRs. */
> +	if (type == -1)
> +		return mtrr_default_type(mtrr_state);
> +
>  	return type;
>  }
>  EXPORT_SYMBOL_GPL(kvm_mtrr_get_guest_memory_type);
> 
> The WARN_ON() now comes before the type == -1 test and I hit that at
> *very* high frequency when trying to test device assignment.  Restoring
> the ordering to what Xiao originally proposed resolves the problem.
> Thanks,

And I remember testing the change and seeing the warning.  So, in short,
I screwed up.  Probably I tested on one machine and pushed from another. :/

Paolo