Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line
On Fri, 01 Oct 2021 10:27:18 +0100,
Suzuki K Poulose wrote:
>
> On 30/09/2021 11:29, Marc Zyngier wrote:
> > On Wed, 29 Sep 2021 11:35:46 +0100,
> > Suzuki K Poulose 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.
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Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line
On 30/09/2021 11:29, Marc Zyngier wrote:
On Wed, 29 Sep 2021 11:35:46 +0100,
Suzuki K Poulose 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
---
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 {
charalias[FTR_ALIAS_NAME_LEN];
charfeature[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
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Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line
On Wed, 29 Sep 2021 11:35:46 +0100,
Suzuki K Poulose 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
> > ---
> > 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 {
> > charalias[FTR_ALIAS_NAME_LEN];
> > charfeature[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
>
Thanks,
M.
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Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line
Hi David,
On Tue, 28 Sep 2021 15:58:08 +0100,
David Brazdil wrote:
>
> Hey Marc,
> that all makes sense:
>
> Reviewed-by: David Brazdil
>
> > @@ -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.
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Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line
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
---
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 {
charalias[FTR_ALIAS_NAME_LEN];
charfeature[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
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Re: [PATCH] KVM: arm64: Allow KVM to be disabled from the command line
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 > --- > 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 ___ kvmarm mailing list 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
Hey Marc,
that all makes sense:
Reviewed-by: David Brazdil
> @@ -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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[PATCH] KVM: arm64: Allow KVM to be disabled from the command line
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
---
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 {
charalias[FTR_ALIAS_NAME_LEN];
charfeature[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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