Re: [PATCH] KVM: MIPS: Change the definition of kvm type

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On 10/09/2020 12.33, Huacai Chen wrote:
> MIPS defines two kvm types:
> 
>  #define KVM_VM_MIPS_TE          0
>  #define KVM_VM_MIPS_VZ          1
> 
> In Documentation/virt/kvm/api.rst it is said that "You probably want to
> use 0 as machine type", which implies that type 0 be the "automatic" or
> "default" type. And, in user-space libvirt use the null-machine (with
> type 0) to detect the kvm capability, which returns "KVM not supported"
> on a VZ platform.
> 
> I try to fix it in QEMU but it is ugly:
> https://lists.nongnu.org/archive/html/qemu-devel/2020-08/msg05629.html
> 
> And Thomas Huth suggests me to change the definition of kvm type:
> https://lists.nongnu.org/archive/html/qemu-devel/2020-09/msg03281.html
> 
> So I define like this:
> 
>  #define KVM_VM_MIPS_AUTO        0
>  #define KVM_VM_MIPS_VZ          1
>  #define KVM_VM_MIPS_TE          2
> 
> Since VZ and TE cannot co-exists, using type 0 on a TE platform will
> still return success (so old user-space tools have no problems on new
> kernels); the advantage is that using type 0 on a VZ platform will not
> return failure. So, the only problem is "new user-space tools use type
> 2 on old kernels", but if we treat this as a kernel bug, we can backport
> this patch to old stable kernels.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Huacai Chen <chenhc@xxxxxxxxxx>
> ---
>  arch/mips/kvm/mips.c     | 2 ++
>  include/uapi/linux/kvm.h | 5 +++--
>  2 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
> index d7ba3f9..9efeb67 100644
> --- a/arch/mips/kvm/mips.c
> +++ b/arch/mips/kvm/mips.c
> @@ -138,6 +138,8 @@ extern void kvm_init_loongson_ipi(struct kvm *kvm);
>  int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>  {
>  	switch (type) {
> +	case KVM_VM_MIPS_AUTO:
> +		break;
>  #ifdef CONFIG_KVM_MIPS_VZ
>  	case KVM_VM_MIPS_VZ:
>  #else
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 29ba8e8..cfc1ae2 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -790,9 +790,10 @@ struct kvm_ppc_resize_hpt {
>  #define KVM_VM_PPC_HV 1
>  #define KVM_VM_PPC_PR 2
>  
> -/* on MIPS, 0 forces trap & emulate, 1 forces VZ ASE */
> -#define KVM_VM_MIPS_TE		0
> +/* on MIPS, 0 indicates auto, 1 forces VZ ASE, 2 forces trap & emulate */
> +#define KVM_VM_MIPS_AUTO	0
>  #define KVM_VM_MIPS_VZ		1
> +#define KVM_VM_MIPS_TE		2
>  
>  #define KVM_S390_SIE_PAGE_OFFSET 1

Thanks, I think that's the right way to go if we don't want mips to
behave completely different compared to the other architectures (e.g.
powerpc is also using 0 as "automatic" type in arch/powerpc/kvm/powerpc.c).

Reviewed-by: Thomas Huth <thuth@xxxxxxxxxx>




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