[PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Marc Zyngier]

Although KVM can be compiled out of the kernel, it cannot be disabled
at runtime. Allow this possibility by introducing a new mode that
will prevent KVM from initialising.

This is useful in the (limited) circumstances where you don't want
KVM to be available (what is wrong with you?), or when you want
to install another hypervisor instead (good luck with that).

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 Documentation/admin-guide/kernel-parameters.txt |  3 +++
 arch/arm64/include/asm/kvm_host.h               |  1 +
 arch/arm64/kernel/idreg-override.c              |  1 +
 arch/arm64/kvm/arm.c                            | 14 +++++++++++++-
 4 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 91ba391f9b32..cc5f68846434 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2365,6 +2365,9 @@
 	kvm-arm.mode=
 			[KVM,ARM] Select one of KVM/arm64's modes of operation.
 
+			none: Forcefully disable KVM and run in nVHE mode,
+			      preventing KVM from ever initialising.
+
 			nvhe: Standard nVHE-based mode, without support for
 			      protected guests.
 
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index f8be56d5342b..019490c67976 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -58,6 +58,7 @@
 enum kvm_mode {
 	KVM_MODE_DEFAULT,
 	KVM_MODE_PROTECTED,
+	KVM_MODE_NONE,
 };
 enum kvm_mode kvm_get_mode(void);
 
diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
index d8e606fe3c21..57013c1b6552 100644
--- a/arch/arm64/kernel/idreg-override.c
+++ b/arch/arm64/kernel/idreg-override.c
@@ -95,6 +95,7 @@ static const struct {
 	char	alias[FTR_ALIAS_NAME_LEN];
 	char	feature[FTR_ALIAS_OPTION_LEN];
 } aliases[] __initconst = {
+	{ "kvm-arm.mode=none",		"id_aa64mmfr1.vh=0" },
 	{ "kvm-arm.mode=nvhe",		"id_aa64mmfr1.vh=0" },
 	{ "kvm-arm.mode=protected",	"id_aa64mmfr1.vh=0" },
 	{ "arm64.nobti",		"id_aa64pfr1.bt=0" },
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index fe102cd2e518..cdc70e238316 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -2064,6 +2064,11 @@ int kvm_arch_init(void *opaque)
 		return -ENODEV;
 	}
 
+	if (kvm_get_mode() == KVM_MODE_NONE) {
+		kvm_info("KVM disabled from command line\n");
+		return -ENODEV;
+	}
+
 	in_hyp_mode = is_kernel_in_hyp_mode();
 
 	if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE) ||
@@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg)
 		return 0;
 	}
 
-	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode()))
+	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
+		kvm_mode = KVM_MODE_DEFAULT;
 		return 0;
+	}
+
+	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
+		kvm_mode = KVM_MODE_NONE;
+		return 0;
+	}
 
 	return -EINVAL;
 }
-- 
2.30.2

[PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Marc Zyngier]

Although KVM can be compiled out of the kernel, it cannot be disabled
at runtime. Allow this possibility by introducing a new mode that
will prevent KVM from initialising.

This is useful in the (limited) circumstances where you don't want
KVM to be available (what is wrong with you?), or when you want
to install another hypervisor instead (good luck with that).

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 Documentation/admin-guide/kernel-parameters.txt |  3 +++
 arch/arm64/include/asm/kvm_host.h               |  1 +
 arch/arm64/kernel/idreg-override.c              |  1 +
 arch/arm64/kvm/arm.c                            | 14 +++++++++++++-
 4 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 91ba391f9b32..cc5f68846434 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2365,6 +2365,9 @@
 	kvm-arm.mode=
 			[KVM,ARM] Select one of KVM/arm64's modes of operation.
 
+			none: Forcefully disable KVM and run in nVHE mode,
+			      preventing KVM from ever initialising.
+
 			nvhe: Standard nVHE-based mode, without support for
 			      protected guests.
 
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index f8be56d5342b..019490c67976 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -58,6 +58,7 @@
 enum kvm_mode {
 	KVM_MODE_DEFAULT,
 	KVM_MODE_PROTECTED,
+	KVM_MODE_NONE,
 };
 enum kvm_mode kvm_get_mode(void);
 
diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
index d8e606fe3c21..57013c1b6552 100644
--- a/arch/arm64/kernel/idreg-override.c
+++ b/arch/arm64/kernel/idreg-override.c
@@ -95,6 +95,7 @@ static const struct {
 	char	alias[FTR_ALIAS_NAME_LEN];
 	char	feature[FTR_ALIAS_OPTION_LEN];
 } aliases[] __initconst = {
+	{ "kvm-arm.mode=none",		"id_aa64mmfr1.vh=0" },
 	{ "kvm-arm.mode=nvhe",		"id_aa64mmfr1.vh=0" },
 	{ "kvm-arm.mode=protected",	"id_aa64mmfr1.vh=0" },
 	{ "arm64.nobti",		"id_aa64pfr1.bt=0" },
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index fe102cd2e518..cdc70e238316 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -2064,6 +2064,11 @@ int kvm_arch_init(void *opaque)
 		return -ENODEV;
 	}
 
+	if (kvm_get_mode() == KVM_MODE_NONE) {
+		kvm_info("KVM disabled from command line\n");
+		return -ENODEV;
+	}
+
 	in_hyp_mode = is_kernel_in_hyp_mode();
 
 	if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE) ||
@@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg)
 		return 0;
 	}
 
-	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode()))
+	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
+		kvm_mode = KVM_MODE_DEFAULT;
 		return 0;
+	}
+
+	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
+		kvm_mode = KVM_MODE_NONE;
+		return 0;
+	}
 
 	return -EINVAL;
 }
-- 
2.30.2

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https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

[PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Marc Zyngier]

Although KVM can be compiled out of the kernel, it cannot be disabled
at runtime. Allow this possibility by introducing a new mode that
will prevent KVM from initialising.

This is useful in the (limited) circumstances where you don't want
KVM to be available (what is wrong with you?), or when you want
to install another hypervisor instead (good luck with that).

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 Documentation/admin-guide/kernel-parameters.txt |  3 +++
 arch/arm64/include/asm/kvm_host.h               |  1 +
 arch/arm64/kernel/idreg-override.c              |  1 +
 arch/arm64/kvm/arm.c                            | 14 +++++++++++++-
 4 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 91ba391f9b32..cc5f68846434 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2365,6 +2365,9 @@
 	kvm-arm.mode=
 			[KVM,ARM] Select one of KVM/arm64's modes of operation.
 
+			none: Forcefully disable KVM and run in nVHE mode,
+			      preventing KVM from ever initialising.
+
 			nvhe: Standard nVHE-based mode, without support for
 			      protected guests.
 
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index f8be56d5342b..019490c67976 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -58,6 +58,7 @@
 enum kvm_mode {
 	KVM_MODE_DEFAULT,
 	KVM_MODE_PROTECTED,
+	KVM_MODE_NONE,
 };
 enum kvm_mode kvm_get_mode(void);
 
diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
index d8e606fe3c21..57013c1b6552 100644
--- a/arch/arm64/kernel/idreg-override.c
+++ b/arch/arm64/kernel/idreg-override.c
@@ -95,6 +95,7 @@ static const struct {
 	char	alias[FTR_ALIAS_NAME_LEN];
 	char	feature[FTR_ALIAS_OPTION_LEN];
 } aliases[] __initconst = {
+	{ "kvm-arm.mode=none",		"id_aa64mmfr1.vh=0" },
 	{ "kvm-arm.mode=nvhe",		"id_aa64mmfr1.vh=0" },
 	{ "kvm-arm.mode=protected",	"id_aa64mmfr1.vh=0" },
 	{ "arm64.nobti",		"id_aa64pfr1.bt=0" },
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index fe102cd2e518..cdc70e238316 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -2064,6 +2064,11 @@ int kvm_arch_init(void *opaque)
 		return -ENODEV;
 	}
 
+	if (kvm_get_mode() == KVM_MODE_NONE) {
+		kvm_info("KVM disabled from command line\n");
+		return -ENODEV;
+	}
+
 	in_hyp_mode = is_kernel_in_hyp_mode();
 
 	if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE) ||
@@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg)
 		return 0;
 	}
 
-	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode()))
+	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
+		kvm_mode = KVM_MODE_DEFAULT;
 		return 0;
+	}
+
+	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
+		kvm_mode = KVM_MODE_NONE;
+		return 0;
+	}
 
 	return -EINVAL;
 }
-- 
2.30.2


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Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[David Brazdil]

Hey Marc,
that all makes sense:

Reviewed-by: David Brazdil <dbrazdil@google.com>

> @@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg)
>  		return 0;
>  	}
>  
> -	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode()))
> +	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> +		kvm_mode = KVM_MODE_DEFAULT;
>  		return 0;
> +	}
> +
> +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
nit: I noticed we check is_kernel_in_hyp_mode here for nvhe/none but for
protected it is checked in is_kvm_protected_mode. May be worth unifying?

Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[David Brazdil]

Hey Marc,
that all makes sense:

Reviewed-by: David Brazdil <dbrazdil@google.com>

> @@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg)
>  		return 0;
>  	}
>  
> -	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode()))
> +	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> +		kvm_mode = KVM_MODE_DEFAULT;
>  		return 0;
> +	}
> +
> +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
nit: I noticed we check is_kernel_in_hyp_mode here for nvhe/none but for
protected it is checked in is_kvm_protected_mode. May be worth unifying?

_______________________________________________
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https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[David Brazdil]

Hey Marc,
that all makes sense:

Reviewed-by: David Brazdil <dbrazdil@google.com>

> @@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg)
>  		return 0;
>  	}
>  
> -	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode()))
> +	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> +		kvm_mode = KVM_MODE_DEFAULT;
>  		return 0;
> +	}
> +
> +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
nit: I noticed we check is_kernel_in_hyp_mode here for nvhe/none but for
protected it is checked in is_kvm_protected_mode. May be worth unifying?


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Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Will Deacon]

On Fri, Sep 03, 2021 at 10:16:52AM +0100, Marc Zyngier wrote:
> Although KVM can be compiled out of the kernel, it cannot be disabled
> at runtime. Allow this possibility by introducing a new mode that
> will prevent KVM from initialising.
> 
> This is useful in the (limited) circumstances where you don't want
> KVM to be available (what is wrong with you?), or when you want
> to install another hypervisor instead (good luck with that).
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  3 +++
>  arch/arm64/include/asm/kvm_host.h               |  1 +
>  arch/arm64/kernel/idreg-override.c              |  1 +
>  arch/arm64/kvm/arm.c                            | 14 +++++++++++++-
>  4 files changed, 18 insertions(+), 1 deletion(-)

Acked-by: Will Deacon <will@kernel.org>

Will

Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Will Deacon]

On Fri, Sep 03, 2021 at 10:16:52AM +0100, Marc Zyngier wrote:
> Although KVM can be compiled out of the kernel, it cannot be disabled
> at runtime. Allow this possibility by introducing a new mode that
> will prevent KVM from initialising.
> 
> This is useful in the (limited) circumstances where you don't want
> KVM to be available (what is wrong with you?), or when you want
> to install another hypervisor instead (good luck with that).
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  3 +++
>  arch/arm64/include/asm/kvm_host.h               |  1 +
>  arch/arm64/kernel/idreg-override.c              |  1 +
>  arch/arm64/kvm/arm.c                            | 14 +++++++++++++-
>  4 files changed, 18 insertions(+), 1 deletion(-)

Acked-by: Will Deacon <will@kernel.org>

Will
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Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Will Deacon]

On Fri, Sep 03, 2021 at 10:16:52AM +0100, Marc Zyngier wrote:
> Although KVM can be compiled out of the kernel, it cannot be disabled
> at runtime. Allow this possibility by introducing a new mode that
> will prevent KVM from initialising.
> 
> This is useful in the (limited) circumstances where you don't want
> KVM to be available (what is wrong with you?), or when you want
> to install another hypervisor instead (good luck with that).
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  3 +++
>  arch/arm64/include/asm/kvm_host.h               |  1 +
>  arch/arm64/kernel/idreg-override.c              |  1 +
>  arch/arm64/kvm/arm.c                            | 14 +++++++++++++-
>  4 files changed, 18 insertions(+), 1 deletion(-)

Acked-by: Will Deacon <will@kernel.org>

Will

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Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Suzuki K Poulose]

On 03/09/2021 10:16, Marc Zyngier wrote:
> Although KVM can be compiled out of the kernel, it cannot be disabled
> at runtime. Allow this possibility by introducing a new mode that
> will prevent KVM from initialising.
> 
> This is useful in the (limited) circumstances where you don't want
> KVM to be available (what is wrong with you?), or when you want
> to install another hypervisor instead (good luck with that).
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>   Documentation/admin-guide/kernel-parameters.txt |  3 +++
>   arch/arm64/include/asm/kvm_host.h               |  1 +
>   arch/arm64/kernel/idreg-override.c              |  1 +
>   arch/arm64/kvm/arm.c                            | 14 +++++++++++++-
>   4 files changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 91ba391f9b32..cc5f68846434 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2365,6 +2365,9 @@
>   	kvm-arm.mode=
>   			[KVM,ARM] Select one of KVM/arm64's modes of operation.
>   
> +			none: Forcefully disable KVM and run in nVHE mode,
> +			      preventing KVM from ever initialising.
> +
>   			nvhe: Standard nVHE-based mode, without support for
>   			      protected guests.
>   
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index f8be56d5342b..019490c67976 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -58,6 +58,7 @@
>   enum kvm_mode {
>   	KVM_MODE_DEFAULT,
>   	KVM_MODE_PROTECTED,
> +	KVM_MODE_NONE,
>   };
>   enum kvm_mode kvm_get_mode(void);
>   
> diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
> index d8e606fe3c21..57013c1b6552 100644
> --- a/arch/arm64/kernel/idreg-override.c
> +++ b/arch/arm64/kernel/idreg-override.c
> @@ -95,6 +95,7 @@ static const struct {
>   	char	alias[FTR_ALIAS_NAME_LEN];
>   	char	feature[FTR_ALIAS_OPTION_LEN];
>   } aliases[] __initconst = {
> +	{ "kvm-arm.mode=none",		"id_aa64mmfr1.vh=0" },
>   	{ "kvm-arm.mode=nvhe",		"id_aa64mmfr1.vh=0" },
>   	{ "kvm-arm.mode=protected",	"id_aa64mmfr1.vh=0" },
>   	{ "arm64.nobti",		"id_aa64pfr1.bt=0" },
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index fe102cd2e518..cdc70e238316 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -2064,6 +2064,11 @@ int kvm_arch_init(void *opaque)
>   		return -ENODEV;
>   	}
>   
> +	if (kvm_get_mode() == KVM_MODE_NONE) {
> +		kvm_info("KVM disabled from command line\n");
> +		return -ENODEV;
> +	}
> +
>   	in_hyp_mode = is_kernel_in_hyp_mode();
>   
>   	if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE) ||
> @@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg)
>   		return 0;
>   	}
>   
> -	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode()))
> +	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> +		kvm_mode = KVM_MODE_DEFAULT;
>   		return 0;
> +	}
> +
> +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {

nit: Does this really need to WARN here ? Unlike the "nvhe" case, if the
user wants to keep the KVM out of the picture for, say debugging
something, it is perfectly Ok to allow the kernel to be running at EL2
without having to change the Firmware to alter the landing EL for the
kernel ?

Otherwise,

Acked-by: Suzuki K Poulose <suzuki.poulose@arm.com>

Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Suzuki K Poulose]

On 03/09/2021 10:16, Marc Zyngier wrote:
> Although KVM can be compiled out of the kernel, it cannot be disabled
> at runtime. Allow this possibility by introducing a new mode that
> will prevent KVM from initialising.
> 
> This is useful in the (limited) circumstances where you don't want
> KVM to be available (what is wrong with you?), or when you want
> to install another hypervisor instead (good luck with that).
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>   Documentation/admin-guide/kernel-parameters.txt |  3 +++
>   arch/arm64/include/asm/kvm_host.h               |  1 +
>   arch/arm64/kernel/idreg-override.c              |  1 +
>   arch/arm64/kvm/arm.c                            | 14 +++++++++++++-
>   4 files changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 91ba391f9b32..cc5f68846434 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2365,6 +2365,9 @@
>   	kvm-arm.mode=
>   			[KVM,ARM] Select one of KVM/arm64's modes of operation.
>   
> +			none: Forcefully disable KVM and run in nVHE mode,
> +			      preventing KVM from ever initialising.
> +
>   			nvhe: Standard nVHE-based mode, without support for
>   			      protected guests.
>   
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index f8be56d5342b..019490c67976 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -58,6 +58,7 @@
>   enum kvm_mode {
>   	KVM_MODE_DEFAULT,
>   	KVM_MODE_PROTECTED,
> +	KVM_MODE_NONE,
>   };
>   enum kvm_mode kvm_get_mode(void);
>   
> diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
> index d8e606fe3c21..57013c1b6552 100644
> --- a/arch/arm64/kernel/idreg-override.c
> +++ b/arch/arm64/kernel/idreg-override.c
> @@ -95,6 +95,7 @@ static const struct {
>   	char	alias[FTR_ALIAS_NAME_LEN];
>   	char	feature[FTR_ALIAS_OPTION_LEN];
>   } aliases[] __initconst = {
> +	{ "kvm-arm.mode=none",		"id_aa64mmfr1.vh=0" },
>   	{ "kvm-arm.mode=nvhe",		"id_aa64mmfr1.vh=0" },
>   	{ "kvm-arm.mode=protected",	"id_aa64mmfr1.vh=0" },
>   	{ "arm64.nobti",		"id_aa64pfr1.bt=0" },
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index fe102cd2e518..cdc70e238316 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -2064,6 +2064,11 @@ int kvm_arch_init(void *opaque)
>   		return -ENODEV;
>   	}
>   
> +	if (kvm_get_mode() == KVM_MODE_NONE) {
> +		kvm_info("KVM disabled from command line\n");
> +		return -ENODEV;
> +	}
> +
>   	in_hyp_mode = is_kernel_in_hyp_mode();
>   
>   	if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE) ||
> @@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg)
>   		return 0;
>   	}
>   
> -	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode()))
> +	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> +		kvm_mode = KVM_MODE_DEFAULT;
>   		return 0;
> +	}
> +
> +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {

nit: Does this really need to WARN here ? Unlike the "nvhe" case, if the
user wants to keep the KVM out of the picture for, say debugging
something, it is perfectly Ok to allow the kernel to be running at EL2
without having to change the Firmware to alter the landing EL for the
kernel ?

Otherwise,

Acked-by: Suzuki K Poulose <suzuki.poulose@arm.com>
_______________________________________________
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kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Suzuki K Poulose]

On 03/09/2021 10:16, Marc Zyngier wrote:
> Although KVM can be compiled out of the kernel, it cannot be disabled
> at runtime. Allow this possibility by introducing a new mode that
> will prevent KVM from initialising.
> 
> This is useful in the (limited) circumstances where you don't want
> KVM to be available (what is wrong with you?), or when you want
> to install another hypervisor instead (good luck with that).
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>   Documentation/admin-guide/kernel-parameters.txt |  3 +++
>   arch/arm64/include/asm/kvm_host.h               |  1 +
>   arch/arm64/kernel/idreg-override.c              |  1 +
>   arch/arm64/kvm/arm.c                            | 14 +++++++++++++-
>   4 files changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 91ba391f9b32..cc5f68846434 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2365,6 +2365,9 @@
>   	kvm-arm.mode=
>   			[KVM,ARM] Select one of KVM/arm64's modes of operation.
>   
> +			none: Forcefully disable KVM and run in nVHE mode,
> +			      preventing KVM from ever initialising.
> +
>   			nvhe: Standard nVHE-based mode, without support for
>   			      protected guests.
>   
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index f8be56d5342b..019490c67976 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -58,6 +58,7 @@
>   enum kvm_mode {
>   	KVM_MODE_DEFAULT,
>   	KVM_MODE_PROTECTED,
> +	KVM_MODE_NONE,
>   };
>   enum kvm_mode kvm_get_mode(void);
>   
> diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
> index d8e606fe3c21..57013c1b6552 100644
> --- a/arch/arm64/kernel/idreg-override.c
> +++ b/arch/arm64/kernel/idreg-override.c
> @@ -95,6 +95,7 @@ static const struct {
>   	char	alias[FTR_ALIAS_NAME_LEN];
>   	char	feature[FTR_ALIAS_OPTION_LEN];
>   } aliases[] __initconst = {
> +	{ "kvm-arm.mode=none",		"id_aa64mmfr1.vh=0" },
>   	{ "kvm-arm.mode=nvhe",		"id_aa64mmfr1.vh=0" },
>   	{ "kvm-arm.mode=protected",	"id_aa64mmfr1.vh=0" },
>   	{ "arm64.nobti",		"id_aa64pfr1.bt=0" },
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index fe102cd2e518..cdc70e238316 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -2064,6 +2064,11 @@ int kvm_arch_init(void *opaque)
>   		return -ENODEV;
>   	}
>   
> +	if (kvm_get_mode() == KVM_MODE_NONE) {
> +		kvm_info("KVM disabled from command line\n");
> +		return -ENODEV;
> +	}
> +
>   	in_hyp_mode = is_kernel_in_hyp_mode();
>   
>   	if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE) ||
> @@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg)
>   		return 0;
>   	}
>   
> -	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode()))
> +	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> +		kvm_mode = KVM_MODE_DEFAULT;
>   		return 0;
> +	}
> +
> +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {

nit: Does this really need to WARN here ? Unlike the "nvhe" case, if the
user wants to keep the KVM out of the picture for, say debugging
something, it is perfectly Ok to allow the kernel to be running at EL2
without having to change the Firmware to alter the landing EL for the
kernel ?

Otherwise,

Acked-by: Suzuki K Poulose <suzuki.poulose@arm.com>

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Marc Zyngier]

Hi David,

On Tue, 28 Sep 2021 15:58:08 +0100,
David Brazdil <dbrazdil@google.com> wrote:
> 
> Hey Marc,
> that all makes sense:
> 
> Reviewed-by: David Brazdil <dbrazdil@google.com>
> 
> > @@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg)
> >  		return 0;
> >  	}
> >  
> > -	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode()))
> > +	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> > +		kvm_mode = KVM_MODE_DEFAULT;
> >  		return 0;
> > +	}
> > +
> > +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> nit: I noticed we check is_kernel_in_hyp_mode here for nvhe/none but for
> protected it is checked in is_kvm_protected_mode. May be worth unifying?

is_kvm_protected_mode() drives a capability (as we rely on the
associated static key), and we don't need this with either 'nvhe' nor
'none'.

So I'm unsure what we can unify, to be honest. Can you suggest a
patch?

Thanks,

	M.

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

Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Marc Zyngier]

Hi David,

On Tue, 28 Sep 2021 15:58:08 +0100,
David Brazdil <dbrazdil@google.com> wrote:
> 
> Hey Marc,
> that all makes sense:
> 
> Reviewed-by: David Brazdil <dbrazdil@google.com>
> 
> > @@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg)
> >  		return 0;
> >  	}
> >  
> > -	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode()))
> > +	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> > +		kvm_mode = KVM_MODE_DEFAULT;
> >  		return 0;
> > +	}
> > +
> > +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> nit: I noticed we check is_kernel_in_hyp_mode here for nvhe/none but for
> protected it is checked in is_kvm_protected_mode. May be worth unifying?

is_kvm_protected_mode() drives a capability (as we rely on the
associated static key), and we don't need this with either 'nvhe' nor
'none'.

So I'm unsure what we can unify, to be honest. Can you suggest a
patch?

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
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Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Marc Zyngier]

Hi David,

On Tue, 28 Sep 2021 15:58:08 +0100,
David Brazdil <dbrazdil@google.com> wrote:
> 
> Hey Marc,
> that all makes sense:
> 
> Reviewed-by: David Brazdil <dbrazdil@google.com>
> 
> > @@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg)
> >  		return 0;
> >  	}
> >  
> > -	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode()))
> > +	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> > +		kvm_mode = KVM_MODE_DEFAULT;
> >  		return 0;
> > +	}
> > +
> > +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> nit: I noticed we check is_kernel_in_hyp_mode here for nvhe/none but for
> protected it is checked in is_kvm_protected_mode. May be worth unifying?

is_kvm_protected_mode() drives a capability (as we rely on the
associated static key), and we don't need this with either 'nvhe' nor
'none'.

So I'm unsure what we can unify, to be honest. Can you suggest a
patch?

Thanks,

	M.

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

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Marc Zyngier]

On Wed, 29 Sep 2021 11:35:46 +0100,
Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
> 
> On 03/09/2021 10:16, Marc Zyngier wrote:
> > Although KVM can be compiled out of the kernel, it cannot be disabled
> > at runtime. Allow this possibility by introducing a new mode that
> > will prevent KVM from initialising.
> > 
> > This is useful in the (limited) circumstances where you don't want
> > KVM to be available (what is wrong with you?), or when you want
> > to install another hypervisor instead (good luck with that).
> > 
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> >   Documentation/admin-guide/kernel-parameters.txt |  3 +++
> >   arch/arm64/include/asm/kvm_host.h               |  1 +
> >   arch/arm64/kernel/idreg-override.c              |  1 +
> >   arch/arm64/kvm/arm.c                            | 14 +++++++++++++-
> >   4 files changed, 18 insertions(+), 1 deletion(-)
> > 
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 91ba391f9b32..cc5f68846434 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -2365,6 +2365,9 @@
> >   	kvm-arm.mode=
> >   			[KVM,ARM] Select one of KVM/arm64's modes of operation.
> >   +			none: Forcefully disable KVM and run in nVHE
> > mode,
> > +			      preventing KVM from ever initialising.
> > +
> >   			nvhe: Standard nVHE-based mode, without support for
> >   			      protected guests.
> >   diff --git a/arch/arm64/include/asm/kvm_host.h
> > b/arch/arm64/include/asm/kvm_host.h
> > index f8be56d5342b..019490c67976 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -58,6 +58,7 @@
> >   enum kvm_mode {
> >   	KVM_MODE_DEFAULT,
> >   	KVM_MODE_PROTECTED,
> > +	KVM_MODE_NONE,
> >   };
> >   enum kvm_mode kvm_get_mode(void);
> >   diff --git a/arch/arm64/kernel/idreg-override.c
> > b/arch/arm64/kernel/idreg-override.c
> > index d8e606fe3c21..57013c1b6552 100644
> > --- a/arch/arm64/kernel/idreg-override.c
> > +++ b/arch/arm64/kernel/idreg-override.c
> > @@ -95,6 +95,7 @@ static const struct {
> >   	char	alias[FTR_ALIAS_NAME_LEN];
> >   	char	feature[FTR_ALIAS_OPTION_LEN];
> >   } aliases[] __initconst = {
> > +	{ "kvm-arm.mode=none",		"id_aa64mmfr1.vh=0" },
> >   	{ "kvm-arm.mode=nvhe",		"id_aa64mmfr1.vh=0" },
> >   	{ "kvm-arm.mode=protected",	"id_aa64mmfr1.vh=0" },
> >   	{ "arm64.nobti",		"id_aa64pfr1.bt=0" },
> > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> > index fe102cd2e518..cdc70e238316 100644
> > --- a/arch/arm64/kvm/arm.c
> > +++ b/arch/arm64/kvm/arm.c
> > @@ -2064,6 +2064,11 @@ int kvm_arch_init(void *opaque)
> >   		return -ENODEV;
> >   	}
> >   +	if (kvm_get_mode() == KVM_MODE_NONE) {
> > +		kvm_info("KVM disabled from command line\n");
> > +		return -ENODEV;
> > +	}
> > +
> >   	in_hyp_mode = is_kernel_in_hyp_mode();
> >     	if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE)
> > ||
> > @@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg)
> >   		return 0;
> >   	}
> >   -	if (strcmp(arg, "nvhe") == 0 &&
> > !WARN_ON(is_kernel_in_hyp_mode()))
> > +	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> > +		kvm_mode = KVM_MODE_DEFAULT;
> >   		return 0;
> > +	}
> > +
> > +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> 
> nit: Does this really need to WARN here ? Unlike the "nvhe" case, if the
> user wants to keep the KVM out of the picture for, say debugging
> something, it is perfectly Ok to allow the kernel to be running at EL2
> without having to change the Firmware to alter the landing EL for the
> kernel ?

Well, the doc says "run in nVHE mode" and the option forces
id_aa64mmfr1.vh=0. The WARN_ON() will only fires on broken^Wfruity HW
that is VHE only. Note that this doesn't rely on any firmware change
(we drop from EL2 to EL1 and stay there).

We could add another option (none-vhe?) that stays at EL2 and still
disables KVM if there is an appetite for it.

> Otherwise,
> 
> Acked-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> 

Thanks,

	M.

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

Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Marc Zyngier]

On Wed, 29 Sep 2021 11:35:46 +0100,
Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
> 
> On 03/09/2021 10:16, Marc Zyngier wrote:
> > Although KVM can be compiled out of the kernel, it cannot be disabled
> > at runtime. Allow this possibility by introducing a new mode that
> > will prevent KVM from initialising.
> > 
> > This is useful in the (limited) circumstances where you don't want
> > KVM to be available (what is wrong with you?), or when you want
> > to install another hypervisor instead (good luck with that).
> > 
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> >   Documentation/admin-guide/kernel-parameters.txt |  3 +++
> >   arch/arm64/include/asm/kvm_host.h               |  1 +
> >   arch/arm64/kernel/idreg-override.c              |  1 +
> >   arch/arm64/kvm/arm.c                            | 14 +++++++++++++-
> >   4 files changed, 18 insertions(+), 1 deletion(-)
> > 
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 91ba391f9b32..cc5f68846434 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -2365,6 +2365,9 @@
> >   	kvm-arm.mode=
> >   			[KVM,ARM] Select one of KVM/arm64's modes of operation.
> >   +			none: Forcefully disable KVM and run in nVHE
> > mode,
> > +			      preventing KVM from ever initialising.
> > +
> >   			nvhe: Standard nVHE-based mode, without support for
> >   			      protected guests.
> >   diff --git a/arch/arm64/include/asm/kvm_host.h
> > b/arch/arm64/include/asm/kvm_host.h
> > index f8be56d5342b..019490c67976 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -58,6 +58,7 @@
> >   enum kvm_mode {
> >   	KVM_MODE_DEFAULT,
> >   	KVM_MODE_PROTECTED,
> > +	KVM_MODE_NONE,
> >   };
> >   enum kvm_mode kvm_get_mode(void);
> >   diff --git a/arch/arm64/kernel/idreg-override.c
> > b/arch/arm64/kernel/idreg-override.c
> > index d8e606fe3c21..57013c1b6552 100644
> > --- a/arch/arm64/kernel/idreg-override.c
> > +++ b/arch/arm64/kernel/idreg-override.c
> > @@ -95,6 +95,7 @@ static const struct {
> >   	char	alias[FTR_ALIAS_NAME_LEN];
> >   	char	feature[FTR_ALIAS_OPTION_LEN];
> >   } aliases[] __initconst = {
> > +	{ "kvm-arm.mode=none",		"id_aa64mmfr1.vh=0" },
> >   	{ "kvm-arm.mode=nvhe",		"id_aa64mmfr1.vh=0" },
> >   	{ "kvm-arm.mode=protected",	"id_aa64mmfr1.vh=0" },
> >   	{ "arm64.nobti",		"id_aa64pfr1.bt=0" },
> > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> > index fe102cd2e518..cdc70e238316 100644
> > --- a/arch/arm64/kvm/arm.c
> > +++ b/arch/arm64/kvm/arm.c
> > @@ -2064,6 +2064,11 @@ int kvm_arch_init(void *opaque)
> >   		return -ENODEV;
> >   	}
> >   +	if (kvm_get_mode() == KVM_MODE_NONE) {
> > +		kvm_info("KVM disabled from command line\n");
> > +		return -ENODEV;
> > +	}
> > +
> >   	in_hyp_mode = is_kernel_in_hyp_mode();
> >     	if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE)
> > ||
> > @@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg)
> >   		return 0;
> >   	}
> >   -	if (strcmp(arg, "nvhe") == 0 &&
> > !WARN_ON(is_kernel_in_hyp_mode()))
> > +	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> > +		kvm_mode = KVM_MODE_DEFAULT;
> >   		return 0;
> > +	}
> > +
> > +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> 
> nit: Does this really need to WARN here ? Unlike the "nvhe" case, if the
> user wants to keep the KVM out of the picture for, say debugging
> something, it is perfectly Ok to allow the kernel to be running at EL2
> without having to change the Firmware to alter the landing EL for the
> kernel ?

Well, the doc says "run in nVHE mode" and the option forces
id_aa64mmfr1.vh=0. The WARN_ON() will only fires on broken^Wfruity HW
that is VHE only. Note that this doesn't rely on any firmware change
(we drop from EL2 to EL1 and stay there).

We could add another option (none-vhe?) that stays at EL2 and still
disables KVM if there is an appetite for it.

> Otherwise,
> 
> Acked-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> 

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.
_______________________________________________
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https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Marc Zyngier]

On Wed, 29 Sep 2021 11:35:46 +0100,
Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
> 
> On 03/09/2021 10:16, Marc Zyngier wrote:
> > Although KVM can be compiled out of the kernel, it cannot be disabled
> > at runtime. Allow this possibility by introducing a new mode that
> > will prevent KVM from initialising.
> > 
> > This is useful in the (limited) circumstances where you don't want
> > KVM to be available (what is wrong with you?), or when you want
> > to install another hypervisor instead (good luck with that).
> > 
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> >   Documentation/admin-guide/kernel-parameters.txt |  3 +++
> >   arch/arm64/include/asm/kvm_host.h               |  1 +
> >   arch/arm64/kernel/idreg-override.c              |  1 +
> >   arch/arm64/kvm/arm.c                            | 14 +++++++++++++-
> >   4 files changed, 18 insertions(+), 1 deletion(-)
> > 
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 91ba391f9b32..cc5f68846434 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -2365,6 +2365,9 @@
> >   	kvm-arm.mode=
> >   			[KVM,ARM] Select one of KVM/arm64's modes of operation.
> >   +			none: Forcefully disable KVM and run in nVHE
> > mode,
> > +			      preventing KVM from ever initialising.
> > +
> >   			nvhe: Standard nVHE-based mode, without support for
> >   			      protected guests.
> >   diff --git a/arch/arm64/include/asm/kvm_host.h
> > b/arch/arm64/include/asm/kvm_host.h
> > index f8be56d5342b..019490c67976 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -58,6 +58,7 @@
> >   enum kvm_mode {
> >   	KVM_MODE_DEFAULT,
> >   	KVM_MODE_PROTECTED,
> > +	KVM_MODE_NONE,
> >   };
> >   enum kvm_mode kvm_get_mode(void);
> >   diff --git a/arch/arm64/kernel/idreg-override.c
> > b/arch/arm64/kernel/idreg-override.c
> > index d8e606fe3c21..57013c1b6552 100644
> > --- a/arch/arm64/kernel/idreg-override.c
> > +++ b/arch/arm64/kernel/idreg-override.c
> > @@ -95,6 +95,7 @@ static const struct {
> >   	char	alias[FTR_ALIAS_NAME_LEN];
> >   	char	feature[FTR_ALIAS_OPTION_LEN];
> >   } aliases[] __initconst = {
> > +	{ "kvm-arm.mode=none",		"id_aa64mmfr1.vh=0" },
> >   	{ "kvm-arm.mode=nvhe",		"id_aa64mmfr1.vh=0" },
> >   	{ "kvm-arm.mode=protected",	"id_aa64mmfr1.vh=0" },
> >   	{ "arm64.nobti",		"id_aa64pfr1.bt=0" },
> > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> > index fe102cd2e518..cdc70e238316 100644
> > --- a/arch/arm64/kvm/arm.c
> > +++ b/arch/arm64/kvm/arm.c
> > @@ -2064,6 +2064,11 @@ int kvm_arch_init(void *opaque)
> >   		return -ENODEV;
> >   	}
> >   +	if (kvm_get_mode() == KVM_MODE_NONE) {
> > +		kvm_info("KVM disabled from command line\n");
> > +		return -ENODEV;
> > +	}
> > +
> >   	in_hyp_mode = is_kernel_in_hyp_mode();
> >     	if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE)
> > ||
> > @@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg)
> >   		return 0;
> >   	}
> >   -	if (strcmp(arg, "nvhe") == 0 &&
> > !WARN_ON(is_kernel_in_hyp_mode()))
> > +	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> > +		kvm_mode = KVM_MODE_DEFAULT;
> >   		return 0;
> > +	}
> > +
> > +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> 
> nit: Does this really need to WARN here ? Unlike the "nvhe" case, if the
> user wants to keep the KVM out of the picture for, say debugging
> something, it is perfectly Ok to allow the kernel to be running at EL2
> without having to change the Firmware to alter the landing EL for the
> kernel ?

Well, the doc says "run in nVHE mode" and the option forces
id_aa64mmfr1.vh=0. The WARN_ON() will only fires on broken^Wfruity HW
that is VHE only. Note that this doesn't rely on any firmware change
(we drop from EL2 to EL1 and stay there).

We could add another option (none-vhe?) that stays at EL2 and still
disables KVM if there is an appetite for it.

> Otherwise,
> 
> Acked-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> 

Thanks,

	M.

-- 
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Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Suzuki K Poulose]

On 30/09/2021 11:29, Marc Zyngier wrote:
> On Wed, 29 Sep 2021 11:35:46 +0100,
> Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
>>
>> On 03/09/2021 10:16, Marc Zyngier wrote:
>>> Although KVM can be compiled out of the kernel, it cannot be disabled
>>> at runtime. Allow this possibility by introducing a new mode that
>>> will prevent KVM from initialising.
>>>
>>> This is useful in the (limited) circumstances where you don't want
>>> KVM to be available (what is wrong with you?), or when you want
>>> to install another hypervisor instead (good luck with that).
>>>
>>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>>> ---
>>>    Documentation/admin-guide/kernel-parameters.txt |  3 +++
>>>    arch/arm64/include/asm/kvm_host.h               |  1 +
>>>    arch/arm64/kernel/idreg-override.c              |  1 +
>>>    arch/arm64/kvm/arm.c                            | 14 +++++++++++++-
>>>    4 files changed, 18 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>>> index 91ba391f9b32..cc5f68846434 100644
>>> --- a/Documentation/admin-guide/kernel-parameters.txt
>>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>>> @@ -2365,6 +2365,9 @@
>>>    	kvm-arm.mode=
>>>    			[KVM,ARM] Select one of KVM/arm64's modes of operation.
>>>    +			none: Forcefully disable KVM and run in nVHE
>>> mode,
>>> +			      preventing KVM from ever initialising.
>>> +
>>>    			nvhe: Standard nVHE-based mode, without support for
>>>    			      protected guests.
>>>    diff --git a/arch/arm64/include/asm/kvm_host.h
>>> b/arch/arm64/include/asm/kvm_host.h
>>> index f8be56d5342b..019490c67976 100644
>>> --- a/arch/arm64/include/asm/kvm_host.h
>>> +++ b/arch/arm64/include/asm/kvm_host.h
>>> @@ -58,6 +58,7 @@
>>>    enum kvm_mode {
>>>    	KVM_MODE_DEFAULT,
>>>    	KVM_MODE_PROTECTED,
>>> +	KVM_MODE_NONE,
>>>    };
>>>    enum kvm_mode kvm_get_mode(void);
>>>    diff --git a/arch/arm64/kernel/idreg-override.c
>>> b/arch/arm64/kernel/idreg-override.c
>>> index d8e606fe3c21..57013c1b6552 100644
>>> --- a/arch/arm64/kernel/idreg-override.c
>>> +++ b/arch/arm64/kernel/idreg-override.c
>>> @@ -95,6 +95,7 @@ static const struct {
>>>    	char	alias[FTR_ALIAS_NAME_LEN];
>>>    	char	feature[FTR_ALIAS_OPTION_LEN];
>>>    } aliases[] __initconst = {
>>> +	{ "kvm-arm.mode=none",		"id_aa64mmfr1.vh=0" },
>>>    	{ "kvm-arm.mode=nvhe",		"id_aa64mmfr1.vh=0" },
>>>    	{ "kvm-arm.mode=protected",	"id_aa64mmfr1.vh=0" },
>>>    	{ "arm64.nobti",		"id_aa64pfr1.bt=0" },
>>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>>> index fe102cd2e518..cdc70e238316 100644
>>> --- a/arch/arm64/kvm/arm.c
>>> +++ b/arch/arm64/kvm/arm.c
>>> @@ -2064,6 +2064,11 @@ int kvm_arch_init(void *opaque)
>>>    		return -ENODEV;
>>>    	}
>>>    +	if (kvm_get_mode() == KVM_MODE_NONE) {
>>> +		kvm_info("KVM disabled from command line\n");
>>> +		return -ENODEV;
>>> +	}
>>> +
>>>    	in_hyp_mode = is_kernel_in_hyp_mode();
>>>      	if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE)
>>> ||
>>> @@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg)
>>>    		return 0;
>>>    	}
>>>    -	if (strcmp(arg, "nvhe") == 0 &&
>>> !WARN_ON(is_kernel_in_hyp_mode()))
>>> +	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
>>> +		kvm_mode = KVM_MODE_DEFAULT;
>>>    		return 0;
>>> +	}
>>> +
>>> +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
>>
>> nit: Does this really need to WARN here ? Unlike the "nvhe" case, if the
>> user wants to keep the KVM out of the picture for, say debugging
>> something, it is perfectly Ok to allow the kernel to be running at EL2
>> without having to change the Firmware to alter the landing EL for the
>> kernel ?
> 
> Well, the doc says "run in nVHE mode" and the option forces
> id_aa64mmfr1.vh=0. The WARN_ON() will only fires on broken^Wfruity HW
> that is VHE only. Note that this doesn't rely on any firmware change
> (we drop from EL2 to EL1 and stay there).

Ah, ok. So the "none" is in fact "nvhe + no-kvm". Thats the bit I
missed. TBH, that name to me sounds like "no KVM" at all, which is what
we want. The question is, do we really need "none" to force vh == 0 ? I
understand this is only a problem on a rare set of HWs. But the generic
option looks deceiving.

That said, I am happy to leave this as is and the doc says so.

> 
> We could add another option (none-vhe?) that stays at EL2 and still
> disables KVM if there is an appetite for it.

Na. Don't think that is necessary.

> 
>> Otherwise,
>>
>> Acked-by: Suzuki K Poulose <suzuki.poulose@arm.com>

Suzuki

Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Suzuki K Poulose]

On 30/09/2021 11:29, Marc Zyngier wrote:
> On Wed, 29 Sep 2021 11:35:46 +0100,
> Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
>>
>> On 03/09/2021 10:16, Marc Zyngier wrote:
>>> Although KVM can be compiled out of the kernel, it cannot be disabled
>>> at runtime. Allow this possibility by introducing a new mode that
>>> will prevent KVM from initialising.
>>>
>>> This is useful in the (limited) circumstances where you don't want
>>> KVM to be available (what is wrong with you?), or when you want
>>> to install another hypervisor instead (good luck with that).
>>>
>>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>>> ---
>>>    Documentation/admin-guide/kernel-parameters.txt |  3 +++
>>>    arch/arm64/include/asm/kvm_host.h               |  1 +
>>>    arch/arm64/kernel/idreg-override.c              |  1 +
>>>    arch/arm64/kvm/arm.c                            | 14 +++++++++++++-
>>>    4 files changed, 18 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>>> index 91ba391f9b32..cc5f68846434 100644
>>> --- a/Documentation/admin-guide/kernel-parameters.txt
>>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>>> @@ -2365,6 +2365,9 @@
>>>    	kvm-arm.mode=
>>>    			[KVM,ARM] Select one of KVM/arm64's modes of operation.
>>>    +			none: Forcefully disable KVM and run in nVHE
>>> mode,
>>> +			      preventing KVM from ever initialising.
>>> +
>>>    			nvhe: Standard nVHE-based mode, without support for
>>>    			      protected guests.
>>>    diff --git a/arch/arm64/include/asm/kvm_host.h
>>> b/arch/arm64/include/asm/kvm_host.h
>>> index f8be56d5342b..019490c67976 100644
>>> --- a/arch/arm64/include/asm/kvm_host.h
>>> +++ b/arch/arm64/include/asm/kvm_host.h
>>> @@ -58,6 +58,7 @@
>>>    enum kvm_mode {
>>>    	KVM_MODE_DEFAULT,
>>>    	KVM_MODE_PROTECTED,
>>> +	KVM_MODE_NONE,
>>>    };
>>>    enum kvm_mode kvm_get_mode(void);
>>>    diff --git a/arch/arm64/kernel/idreg-override.c
>>> b/arch/arm64/kernel/idreg-override.c
>>> index d8e606fe3c21..57013c1b6552 100644
>>> --- a/arch/arm64/kernel/idreg-override.c
>>> +++ b/arch/arm64/kernel/idreg-override.c
>>> @@ -95,6 +95,7 @@ static const struct {
>>>    	char	alias[FTR_ALIAS_NAME_LEN];
>>>    	char	feature[FTR_ALIAS_OPTION_LEN];
>>>    } aliases[] __initconst = {
>>> +	{ "kvm-arm.mode=none",		"id_aa64mmfr1.vh=0" },
>>>    	{ "kvm-arm.mode=nvhe",		"id_aa64mmfr1.vh=0" },
>>>    	{ "kvm-arm.mode=protected",	"id_aa64mmfr1.vh=0" },
>>>    	{ "arm64.nobti",		"id_aa64pfr1.bt=0" },
>>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>>> index fe102cd2e518..cdc70e238316 100644
>>> --- a/arch/arm64/kvm/arm.c
>>> +++ b/arch/arm64/kvm/arm.c
>>> @@ -2064,6 +2064,11 @@ int kvm_arch_init(void *opaque)
>>>    		return -ENODEV;
>>>    	}
>>>    +	if (kvm_get_mode() == KVM_MODE_NONE) {
>>> +		kvm_info("KVM disabled from command line\n");
>>> +		return -ENODEV;
>>> +	}
>>> +
>>>    	in_hyp_mode = is_kernel_in_hyp_mode();
>>>      	if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE)
>>> ||
>>> @@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg)
>>>    		return 0;
>>>    	}
>>>    -	if (strcmp(arg, "nvhe") == 0 &&
>>> !WARN_ON(is_kernel_in_hyp_mode()))
>>> +	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
>>> +		kvm_mode = KVM_MODE_DEFAULT;
>>>    		return 0;
>>> +	}
>>> +
>>> +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
>>
>> nit: Does this really need to WARN here ? Unlike the "nvhe" case, if the
>> user wants to keep the KVM out of the picture for, say debugging
>> something, it is perfectly Ok to allow the kernel to be running at EL2
>> without having to change the Firmware to alter the landing EL for the
>> kernel ?
> 
> Well, the doc says "run in nVHE mode" and the option forces
> id_aa64mmfr1.vh=0. The WARN_ON() will only fires on broken^Wfruity HW
> that is VHE only. Note that this doesn't rely on any firmware change
> (we drop from EL2 to EL1 and stay there).

Ah, ok. So the "none" is in fact "nvhe + no-kvm". Thats the bit I
missed. TBH, that name to me sounds like "no KVM" at all, which is what
we want. The question is, do we really need "none" to force vh == 0 ? I
understand this is only a problem on a rare set of HWs. But the generic
option looks deceiving.

That said, I am happy to leave this as is and the doc says so.

> 
> We could add another option (none-vhe?) that stays at EL2 and still
> disables KVM if there is an appetite for it.

Na. Don't think that is necessary.

> 
>> Otherwise,
>>
>> Acked-by: Suzuki K Poulose <suzuki.poulose@arm.com>

Suzuki
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Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Suzuki K Poulose]

On 30/09/2021 11:29, Marc Zyngier wrote:
> On Wed, 29 Sep 2021 11:35:46 +0100,
> Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
>>
>> On 03/09/2021 10:16, Marc Zyngier wrote:
>>> Although KVM can be compiled out of the kernel, it cannot be disabled
>>> at runtime. Allow this possibility by introducing a new mode that
>>> will prevent KVM from initialising.
>>>
>>> This is useful in the (limited) circumstances where you don't want
>>> KVM to be available (what is wrong with you?), or when you want
>>> to install another hypervisor instead (good luck with that).
>>>
>>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>>> ---
>>>    Documentation/admin-guide/kernel-parameters.txt |  3 +++
>>>    arch/arm64/include/asm/kvm_host.h               |  1 +
>>>    arch/arm64/kernel/idreg-override.c              |  1 +
>>>    arch/arm64/kvm/arm.c                            | 14 +++++++++++++-
>>>    4 files changed, 18 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>>> index 91ba391f9b32..cc5f68846434 100644
>>> --- a/Documentation/admin-guide/kernel-parameters.txt
>>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>>> @@ -2365,6 +2365,9 @@
>>>    	kvm-arm.mode=
>>>    			[KVM,ARM] Select one of KVM/arm64's modes of operation.
>>>    +			none: Forcefully disable KVM and run in nVHE
>>> mode,
>>> +			      preventing KVM from ever initialising.
>>> +
>>>    			nvhe: Standard nVHE-based mode, without support for
>>>    			      protected guests.
>>>    diff --git a/arch/arm64/include/asm/kvm_host.h
>>> b/arch/arm64/include/asm/kvm_host.h
>>> index f8be56d5342b..019490c67976 100644
>>> --- a/arch/arm64/include/asm/kvm_host.h
>>> +++ b/arch/arm64/include/asm/kvm_host.h
>>> @@ -58,6 +58,7 @@
>>>    enum kvm_mode {
>>>    	KVM_MODE_DEFAULT,
>>>    	KVM_MODE_PROTECTED,
>>> +	KVM_MODE_NONE,
>>>    };
>>>    enum kvm_mode kvm_get_mode(void);
>>>    diff --git a/arch/arm64/kernel/idreg-override.c
>>> b/arch/arm64/kernel/idreg-override.c
>>> index d8e606fe3c21..57013c1b6552 100644
>>> --- a/arch/arm64/kernel/idreg-override.c
>>> +++ b/arch/arm64/kernel/idreg-override.c
>>> @@ -95,6 +95,7 @@ static const struct {
>>>    	char	alias[FTR_ALIAS_NAME_LEN];
>>>    	char	feature[FTR_ALIAS_OPTION_LEN];
>>>    } aliases[] __initconst = {
>>> +	{ "kvm-arm.mode=none",		"id_aa64mmfr1.vh=0" },
>>>    	{ "kvm-arm.mode=nvhe",		"id_aa64mmfr1.vh=0" },
>>>    	{ "kvm-arm.mode=protected",	"id_aa64mmfr1.vh=0" },
>>>    	{ "arm64.nobti",		"id_aa64pfr1.bt=0" },
>>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>>> index fe102cd2e518..cdc70e238316 100644
>>> --- a/arch/arm64/kvm/arm.c
>>> +++ b/arch/arm64/kvm/arm.c
>>> @@ -2064,6 +2064,11 @@ int kvm_arch_init(void *opaque)
>>>    		return -ENODEV;
>>>    	}
>>>    +	if (kvm_get_mode() == KVM_MODE_NONE) {
>>> +		kvm_info("KVM disabled from command line\n");
>>> +		return -ENODEV;
>>> +	}
>>> +
>>>    	in_hyp_mode = is_kernel_in_hyp_mode();
>>>      	if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE)
>>> ||
>>> @@ -2137,8 +2142,15 @@ static int __init early_kvm_mode_cfg(char *arg)
>>>    		return 0;
>>>    	}
>>>    -	if (strcmp(arg, "nvhe") == 0 &&
>>> !WARN_ON(is_kernel_in_hyp_mode()))
>>> +	if (strcmp(arg, "nvhe") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
>>> +		kvm_mode = KVM_MODE_DEFAULT;
>>>    		return 0;
>>> +	}
>>> +
>>> +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
>>
>> nit: Does this really need to WARN here ? Unlike the "nvhe" case, if the
>> user wants to keep the KVM out of the picture for, say debugging
>> something, it is perfectly Ok to allow the kernel to be running at EL2
>> without having to change the Firmware to alter the landing EL for the
>> kernel ?
> 
> Well, the doc says "run in nVHE mode" and the option forces
> id_aa64mmfr1.vh=0. The WARN_ON() will only fires on broken^Wfruity HW
> that is VHE only. Note that this doesn't rely on any firmware change
> (we drop from EL2 to EL1 and stay there).

Ah, ok. So the "none" is in fact "nvhe + no-kvm". Thats the bit I
missed. TBH, that name to me sounds like "no KVM" at all, which is what
we want. The question is, do we really need "none" to force vh == 0 ? I
understand this is only a problem on a rare set of HWs. But the generic
option looks deceiving.

That said, I am happy to leave this as is and the doc says so.

> 
> We could add another option (none-vhe?) that stays at EL2 and still
> disables KVM if there is an appetite for it.

Na. Don't think that is necessary.

> 
>> Otherwise,
>>
>> Acked-by: Suzuki K Poulose <suzuki.poulose@arm.com>

Suzuki

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Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Marc Zyngier]

On Fri, 01 Oct 2021 10:27:18 +0100,
Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
> 
> On 30/09/2021 11:29, Marc Zyngier wrote:
> > On Wed, 29 Sep 2021 11:35:46 +0100,
> > Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
> >> 
> >>> +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> >> 
> >> nit: Does this really need to WARN here ? Unlike the "nvhe" case, if the
> >> user wants to keep the KVM out of the picture for, say debugging
> >> something, it is perfectly Ok to allow the kernel to be running at EL2
> >> without having to change the Firmware to alter the landing EL for the
> >> kernel ?
> > 
> > Well, the doc says "run in nVHE mode" and the option forces
> > id_aa64mmfr1.vh=0. The WARN_ON() will only fires on broken^Wfruity HW
> > that is VHE only. Note that this doesn't rely on any firmware change
> > (we drop from EL2 to EL1 and stay there).
> 
> Ah, ok. So the "none" is in fact "nvhe + no-kvm". Thats the bit I
> missed. TBH, that name to me sounds like "no KVM" at all, which is what
> we want. The question is, do we really need "none" to force vh == 0 ? I
> understand this is only a problem on a rare set of HWs. But the generic
> option looks deceiving.
> 
> That said, I am happy to leave this as is and the doc says so.

I think you have a point here. Conflating the two things is a bit odd,
and we might as well let the user pick the configuration they want
(they can always pass 'id_aa64mmfr1.vh=0' themselves).

I'll respin the patch with this change.

Thanks,

	M.

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

Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Marc Zyngier]

On Fri, 01 Oct 2021 10:27:18 +0100,
Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
> 
> On 30/09/2021 11:29, Marc Zyngier wrote:
> > On Wed, 29 Sep 2021 11:35:46 +0100,
> > Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
> >> 
> >>> +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> >> 
> >> nit: Does this really need to WARN here ? Unlike the "nvhe" case, if the
> >> user wants to keep the KVM out of the picture for, say debugging
> >> something, it is perfectly Ok to allow the kernel to be running at EL2
> >> without having to change the Firmware to alter the landing EL for the
> >> kernel ?
> > 
> > Well, the doc says "run in nVHE mode" and the option forces
> > id_aa64mmfr1.vh=0. The WARN_ON() will only fires on broken^Wfruity HW
> > that is VHE only. Note that this doesn't rely on any firmware change
> > (we drop from EL2 to EL1 and stay there).
> 
> Ah, ok. So the "none" is in fact "nvhe + no-kvm". Thats the bit I
> missed. TBH, that name to me sounds like "no KVM" at all, which is what
> we want. The question is, do we really need "none" to force vh == 0 ? I
> understand this is only a problem on a rare set of HWs. But the generic
> option looks deceiving.
> 
> That said, I am happy to leave this as is and the doc says so.

I think you have a point here. Conflating the two things is a bit odd,
and we might as well let the user pick the configuration they want
(they can always pass 'id_aa64mmfr1.vh=0' themselves).

I'll respin the patch with this change.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.
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Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line

[Marc Zyngier]

On Fri, 01 Oct 2021 10:27:18 +0100,
Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
> 
> On 30/09/2021 11:29, Marc Zyngier wrote:
> > On Wed, 29 Sep 2021 11:35:46 +0100,
> > Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
> >> 
> >>> +	if (strcmp(arg, "none") == 0 && !WARN_ON(is_kernel_in_hyp_mode())) {
> >> 
> >> nit: Does this really need to WARN here ? Unlike the "nvhe" case, if the
> >> user wants to keep the KVM out of the picture for, say debugging
> >> something, it is perfectly Ok to allow the kernel to be running at EL2
> >> without having to change the Firmware to alter the landing EL for the
> >> kernel ?
> > 
> > Well, the doc says "run in nVHE mode" and the option forces
> > id_aa64mmfr1.vh=0. The WARN_ON() will only fires on broken^Wfruity HW
> > that is VHE only. Note that this doesn't rely on any firmware change
> > (we drop from EL2 to EL1 and stay there).
> 
> Ah, ok. So the "none" is in fact "nvhe + no-kvm". Thats the bit I
> missed. TBH, that name to me sounds like "no KVM" at all, which is what
> we want. The question is, do we really need "none" to force vh == 0 ? I
> understand this is only a problem on a rare set of HWs. But the generic
> option looks deceiving.
> 
> That said, I am happy to leave this as is and the doc says so.

I think you have a point here. Conflating the two things is a bit odd,
and we might as well let the user pick the configuration they want
(they can always pass 'id_aa64mmfr1.vh=0' themselves).

I'll respin the patch with this change.

Thanks,

	M.

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

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