[PATCH v2] KVM: nVMX: Fix some comment typos and coding style

[PATCH v2] KVM: nVMX: Fix some comment typos and coding style

[linmiaohe]

From: Miaohe Lin <linmiaohe@huawei.com>

Fix some typos in the comments. Also fix coding style.
[Sean Christopherson rewrites the comment of write_fault_to_shadow_pgtable
field in struct kvm_vcpu_arch.]

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
v1->v2:
Use Sean Christopherson' comment for write_fault_to_shadow_pgtable
---
 arch/x86/include/asm/kvm_host.h | 16 +++++++++++++---
 arch/x86/kvm/vmx/nested.c       |  5 +++--
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 4dffbc10d3f8..40a0c0fd95ca 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -781,9 +781,19 @@ struct kvm_vcpu_arch {
 	u64 msr_kvm_poll_control;
 
 	/*
-	 * Indicate whether the access faults on its page table in guest
-	 * which is set when fix page fault and used to detect unhandeable
-	 * instruction.
+	 * Indicates the guest is trying to write a gfn that contains one or
+	 * more of the PTEs used to translate the write itself, i.e. the access
+	 * is changing its own translation in the guest page tables.  KVM exits
+	 * to userspace if emulation of the faulting instruction fails and this
+	 * flag is set, as KVM cannot make forward progress.
+	 *
+	 * If emulation fails for a write to guest page tables, KVM unprotects
+	 * (zaps) the shadow page for the target gfn and resumes the guest to
+	 * retry the non-emulatable instruction (on hardware).  Unprotecting the
+	 * gfn doesn't allow forward progress for a self-changing access because
+	 * doing so also zaps the translation for the gfn, i.e. retrying the
+	 * instruction will hit a !PRESENT fault, which results in a new shadow
+	 * page and sends KVM back to square one.
 	 */
 	bool write_fault_to_shadow_pgtable;
 
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 657c2eda357c..e7faebccd733 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -544,7 +544,8 @@ static void nested_vmx_disable_intercept_for_msr(unsigned long *msr_bitmap_l1,
 	}
 }
 
-static inline void enable_x2apic_msr_intercepts(unsigned long *msr_bitmap) {
+static inline void enable_x2apic_msr_intercepts(unsigned long *msr_bitmap)
+{
 	int msr;
 
 	for (msr = 0x800; msr <= 0x8ff; msr += BITS_PER_LONG) {
@@ -1981,7 +1982,7 @@ static int nested_vmx_handle_enlightened_vmptrld(struct kvm_vcpu *vcpu,
 	}
 
 	/*
-	 * Clean fields data can't de used on VMLAUNCH and when we switch
+	 * Clean fields data can't be used on VMLAUNCH and when we switch
 	 * between different L2 guests as KVM keeps a single VMCS12 per L1.
 	 */
 	if (from_launch || evmcs_gpa_changed)
-- 
2.19.1

Re: [PATCH v2] KVM: nVMX: Fix some comment typos and coding style

[Vitaly Kuznetsov]

linmiaohe <linmiaohe@huawei.com> writes:

> From: Miaohe Lin <linmiaohe@huawei.com>
>
> Fix some typos in the comments. Also fix coding style.
> [Sean Christopherson rewrites the comment of write_fault_to_shadow_pgtable
> field in struct kvm_vcpu_arch.]
>
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
> v1->v2:
> Use Sean Christopherson' comment for write_fault_to_shadow_pgtable
> ---
>  arch/x86/include/asm/kvm_host.h | 16 +++++++++++++---
>  arch/x86/kvm/vmx/nested.c       |  5 +++--
>  2 files changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 4dffbc10d3f8..40a0c0fd95ca 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -781,9 +781,19 @@ struct kvm_vcpu_arch {
>  	u64 msr_kvm_poll_control;
>  
>  	/*
> -	 * Indicate whether the access faults on its page table in guest
> -	 * which is set when fix page fault and used to detect unhandeable
> -	 * instruction.
> +	 * Indicates the guest is trying to write a gfn that contains one or
> +	 * more of the PTEs used to translate the write itself, i.e. the access
> +	 * is changing its own translation in the guest page tables.  KVM exits
> +	 * to userspace if emulation of the faulting instruction fails and this
> +	 * flag is set, as KVM cannot make forward progress.
> +	 *
> +	 * If emulation fails for a write to guest page tables, KVM unprotects
> +	 * (zaps) the shadow page for the target gfn and resumes the guest to
> +	 * retry the non-emulatable instruction (on hardware).  Unprotecting the
> +	 * gfn doesn't allow forward progress for a self-changing access because
> +	 * doing so also zaps the translation for the gfn, i.e. retrying the
> +	 * instruction will hit a !PRESENT fault, which results in a new shadow
> +	 * page and sends KVM back to square one.
>  	 */
>  	bool write_fault_to_shadow_pgtable;
>  
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 657c2eda357c..e7faebccd733 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -544,7 +544,8 @@ static void nested_vmx_disable_intercept_for_msr(unsigned long *msr_bitmap_l1,
>  	}
>  }
>  
> -static inline void enable_x2apic_msr_intercepts(unsigned long *msr_bitmap) {
> +static inline void enable_x2apic_msr_intercepts(unsigned long *msr_bitmap)
> +{
>  	int msr;
>  
>  	for (msr = 0x800; msr <= 0x8ff; msr += BITS_PER_LONG) {
> @@ -1981,7 +1982,7 @@ static int nested_vmx_handle_enlightened_vmptrld(struct kvm_vcpu *vcpu,
>  	}
>  
>  	/*
> -	 * Clean fields data can't de used on VMLAUNCH and when we switch
> +	 * Clean fields data can't be used on VMLAUNCH and when we switch
>  	 * between different L2 guests as KVM keeps a single VMCS12 per L1.
>  	 */
>  	if (from_launch || evmcs_gpa_changed)

With Sean's comment added the subject of the patch is a bit unexpected
:-) But the change itself looks good (and thanks Sean for the great
explanation!).

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

-- 
Vitaly

Re: [PATCH v2] KVM: nVMX: Fix some comment typos and coding style

[Paolo Bonzini]

On 07/02/20 16:22, linmiaohe wrote:
> From: Miaohe Lin <linmiaohe@huawei.com>
> 
> Fix some typos in the comments. Also fix coding style.
> [Sean Christopherson rewrites the comment of write_fault_to_shadow_pgtable
> field in struct kvm_vcpu_arch.]
> 
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
> v1->v2:
> Use Sean Christopherson' comment for write_fault_to_shadow_pgtable
> ---
>  arch/x86/include/asm/kvm_host.h | 16 +++++++++++++---
>  arch/x86/kvm/vmx/nested.c       |  5 +++--
>  2 files changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 4dffbc10d3f8..40a0c0fd95ca 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -781,9 +781,19 @@ struct kvm_vcpu_arch {
>  	u64 msr_kvm_poll_control;
>  
>  	/*
> -	 * Indicate whether the access faults on its page table in guest
> -	 * which is set when fix page fault and used to detect unhandeable
> -	 * instruction.
> +	 * Indicates the guest is trying to write a gfn that contains one or
> +	 * more of the PTEs used to translate the write itself, i.e. the access
> +	 * is changing its own translation in the guest page tables.  KVM exits
> +	 * to userspace if emulation of the faulting instruction fails and this
> +	 * flag is set, as KVM cannot make forward progress.
> +	 *
> +	 * If emulation fails for a write to guest page tables, KVM unprotects
> +	 * (zaps) the shadow page for the target gfn and resumes the guest to
> +	 * retry the non-emulatable instruction (on hardware).  Unprotecting the
> +	 * gfn doesn't allow forward progress for a self-changing access because
> +	 * doing so also zaps the translation for the gfn, i.e. retrying the
> +	 * instruction will hit a !PRESENT fault, which results in a new shadow
> +	 * page and sends KVM back to square one.
>  	 */
>  	bool write_fault_to_shadow_pgtable;
>  
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 657c2eda357c..e7faebccd733 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -544,7 +544,8 @@ static void nested_vmx_disable_intercept_for_msr(unsigned long *msr_bitmap_l1,
>  	}
>  }
>  
> -static inline void enable_x2apic_msr_intercepts(unsigned long *msr_bitmap) {
> +static inline void enable_x2apic_msr_intercepts(unsigned long *msr_bitmap)
> +{
>  	int msr;
>  
>  	for (msr = 0x800; msr <= 0x8ff; msr += BITS_PER_LONG) {
> @@ -1981,7 +1982,7 @@ static int nested_vmx_handle_enlightened_vmptrld(struct kvm_vcpu *vcpu,
>  	}
>  
>  	/*
> -	 * Clean fields data can't de used on VMLAUNCH and when we switch
> +	 * Clean fields data can't be used on VMLAUNCH and when we switch
>  	 * between different L2 guests as KVM keeps a single VMCS12 per L1.
>  	 */
>  	if (from_launch || evmcs_gpa_changed)
> 

Queued, thanks.

Paolo