Hi Mostafa,
On Thu, 24 Oct 2024 17:06:14 +0100,
Mostafa Saleh <smostafa@xxxxxxxxxx> wrote:
>
> Commit 5053c3f0519c ("KVM: arm64: Use hVHE in pKVM by default on CPUs with
> VHE support") modified the behaviour of "kvm-arm.mode=protected" without
> the updating the kernel parameters doc.
>
> Update it to match the current implementation.
>
> Also, update required architecture version for nested virtualization as
> suggested by Marc.
>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Marc Zyngier <maz@xxxxxxxxxx>
>
> Signed-off-by: Mostafa Saleh <smostafa@xxxxxxxxxx>
>
> ---
> v2: Update nested value also
Thanks for that. However...
> ---
> Documentation/admin-guide/kernel-parameters.txt | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 1518343bbe22..d5b771e5cb5b 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2740,12 +2740,16 @@
> nvhe: Standard nVHE-based mode, without support for
> protected guests.
>
> - protected: nVHE-based mode with support for guests whose
> + protected: hVHE-based mode with support for guests whose
> state is kept private from the host.
> + In case hVHE is not supported in hardware, it will
> + boot with protected nVHE.
> + nVHE protected mode can still be forced on VHE systems
> + using "kvm_arm.mode=protected arm64_sw.hvhe=0 id_aa64mmfr1.vh=0"
I probably didn't explain myself very well. I would like to avoid
mentioning hVHE at all, because this is pretty confusing (and really
an implementation detail). Instead, we can talk about VHE/nVHE, which
are real architectural features.
Also, I just realised that we can use your command-line magic for
downgrading from VHE to nVHE in all cases, so I'd be suggesting
something like this:
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 1518343bbe223..2bb19f1331fed 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2740,8 +2740,9 @@
nvhe: Standard nVHE-based mode, without support for
protected guests.
- protected: nVHE-based mode with support for guests whose
- state is kept private from the host.
+ protected: Mode with support for guests whose state is
+ kept private from the host, using VHE or
+ nVHE depending on HW support.
nested: VHE-based mode with support for nested
virtualization. Requires at least ARMv8.3
@@ -2749,8 +2750,11 @@
Defaults to VHE/nVHE based on hardware support. Setting
mode to "protected" will disable kexec and hibernation
- for the host. "nested" is experimental and should be
- used with extreme caution.
+ for the host. To force nVHE on VHE hardware, add
+ "arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the
+ command-line.
+ "nested" is experimental and should be used with
+ extreme caution.
kvm-arm.vgic_v3_group0_trap=
[KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0
>
> nested: VHE-based mode with support for nested
> - virtualization. Requires at least ARMv8.3
> - hardware.
> + virtualization. Requires at least ARMv8.4
> + hardware (with FEAT_NV2).
That part looks good!
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
