On Sun, 22 Aug 2021 16:25:26 +0100
Marc Zyngier <maz@xxxxxxxxxx> wrote:
Hi Marc,
> There is some value in keeping the IPA space small, as it reduces
> the size of the stage-2 page tables.
>
> Let's compute the required space at VM creation time, and inform
> the kernel of our requirements.
You mentioned some kernel bug in the first version of this patch, I
guess the fix for this is 262b003d059c?
It seems to me that this is somewhat of a regression on older host
kernels, when trying to run a guest with "-m 2048", for instance?
Should we teach kvmtool about this bug, and do a check for the bug
condition, when kvm__register_ram() returns with -EFAULT? And give users
a hint to try with one MB more or less guest RAM? Or maybe try
this automatically?
>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> ---
> arm/aarch64/kvm.c | 20 +++++++++++++++++++-
> 1 file changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/arm/aarch64/kvm.c b/arm/aarch64/kvm.c
> index d03a27f2..4e66a22e 100644
> --- a/arm/aarch64/kvm.c
> +++ b/arm/aarch64/kvm.c
> @@ -3,6 +3,7 @@
> #include <asm/image.h>
>
> #include <linux/byteorder.h>
> +#include <kvm/util.h>
>
> /*
> * Return the TEXT_OFFSET value that the guest kernel expects. Note
> @@ -59,5 +60,22 @@ int kvm__arch_get_ipa_limit(struct kvm *kvm)
>
> int kvm__get_vm_type(struct kvm *kvm)
> {
> - return KVM_VM_TYPE_ARM_IPA_SIZE(kvm__arch_get_ipa_limit(kvm));
> + unsigned int ipa_bits, max_ipa_bits;
> + unsigned long max_ipa;
> +
> + /* If we're running on an old kernel, use 0 as the VM type */
> + max_ipa_bits = kvm__arch_get_ipa_limit(kvm);
> + if (!max_ipa_bits)
> + return 0;
Should this return KVM_VM_TYPE, as it does at the moment? Or is this
more confusing than helpful?
Just a nit anyway, the patch looks correct otherwise:
Reviewed-by: Andre Przywara <andre.przywara@xxxxxxx>
Cheers,
Andre
> +
> + /* Otherwise, compute the minimal required IPA size */
> + max_ipa = ARM_MEMORY_AREA + kvm->cfg.ram_size - 1;
> + ipa_bits = max(32, fls_long(max_ipa));
> + pr_debug("max_ipa %lx ipa_bits %d max_ipa_bits %d",
> + max_ipa, ipa_bits, max_ipa_bits);
> +
> + if (ipa_bits > max_ipa_bits)
> + die("Memory too large for this system (needs %d bits, %d available)", ipa_bits, max_ipa_bits);
> +
> + return KVM_VM_TYPE_ARM_IPA_SIZE(ipa_bits);
> }
_______________________________________________
kvmarm mailing list
kvmarm@xxxxxxxxxxxxxxxxxxxxx
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
