Re: [PATCH 1/2] [hack] reserve bit KVM_HINTS_HOST_PHYS_BITS

[Michael S. Tsirkin]

On Wed, Aug 31, 2022 at 02:50:58PM +0200, Gerd Hoffmann wrote:
> The KVM_HINTS_HOST_PHYS_BITS bit indicates that qemu has host-phys-bits
> turned on.  This implies the guest can actually work with the full
> available physical address space as advertised by CPUID(0x80000008).
> 
> Temporary hack for RfC patch and testing.  This change must actually be
> done in the linux kernel, then picked up by qemu via header file sync.
> 
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  include/standard-headers/asm-x86/kvm_para.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/standard-headers/asm-x86/kvm_para.h 
> b/include/standard-headers/asm-x86/kvm_para.h
> index f0235e58a1d3..105b958c0f56 100644
> --- a/include/standard-headers/asm-x86/kvm_para.h
> +++ b/include/standard-headers/asm-x86/kvm_para.h
> @@ -37,7 +37,8 @@
>  #define KVM_FEATURE_HC_MAP_GPA_RANGE 16
>  #define KVM_FEATURE_MIGRATION_CONTROL        17
>  
> -#define KVM_HINTS_REALTIME      0
> +#define KVM_HINTS_REALTIME              0
> +#define KVM_HINTS_HOST_PHYS_BITS        1
>  
>  /* The last 8 bits are used to indicate how to interpret the flags field
>   * in pvclock structure. If no bits are set, all flags are ignored.


Just a clarification.
I think what the bit means is that physical address size
data in cpuid is valid.
Accordingly I would rename it to

+#define KVM_HINTS_PHYS_ADDRESS_SIZE_DATA_VALID        1


or some such.


> -- 
> 2.37.2