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

[Nathan Chancellor <natechancellor@gmail.com>]

On Mon, Jan 25, 2021 at 01:41:50PM +0800, Yang Weijiang wrote:
> On Sun, Jan 24, 2021 at 02:08:29PM -0700, Nathan Chancellor wrote:
> > 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?
> >
> Hi, Nathan,
> Could you try Paolo's latest patch?
> 
> [PULL 03/31] x86/cpu: Use max host physical address if -cpu max option is applied

Hi Yang,

That is the version of the patch I tried, which has been pulled into the
master branch.

Cheers,
Nathan