Re: [Qemu-devel][PATCH] x86/cpu: Use max host physical address if -cpu max option is applied

[Nathan Chancellor]

On Wed, Jan 13, 2021 at 05:04:30PM +0800, Yang Weijiang wrote:
> QEMU option -cpu max(max_features) means "Enables all features supported by
> the accelerator in the current host", this looks true for all the features
> except guest max physical address width, so add this patch to enable it.
> 
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> ---
>  target/i386/cpu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 35459a38bb..b5943406f7 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -6673,7 +6673,7 @@ static void x86_cpu_realizefn(DeviceState *dev, Error 
> **errp)
>                  warned = true;
>              }
>  
> -            if (cpu->host_phys_bits) {
> +            if (cpu->host_phys_bits || cpu->max_features) {
>                  /* The user asked for us to use the host physical bits */
>                  cpu->phys_bits = host_phys_bits;
>                  if (cpu->host_phys_bits_limit &&
> -- 
> 2.17.2
> 
> 

Hi,

This patch as commit 5a140b255d ("x86/cpu: Use max host physical address
if -cpu max option is applied") prevents me from using '-cpu host' while
booting an i386_defconfig kernel.

$ qemu-system-i386 \
-append console=ttyS0 \
-cpu host \
-display none \
-enable-kvm \
-initrd rootfs.cpio \
-kernel bzImage \
-serial mon:stdio
qemu-system-i386: phys-bits should be between 32 and 36  (but is 48)

Am I expected to pass "-cpu host,host-phys-bits=false" now or did this
do something unexpected?

Cheers,
Nathan