From: Daniel P. Berrangé <berrange@redhat.com>

Booting Fedora kernels with -cpu max hangs very early in boot. Disabling
the la57 CPUID bit fixes the problem. git bisect traced the regression to

  commit 213ff024a2f92020290296cb9dc29c2af3d4a221 (HEAD, refs/bisect/bad)
  Author: Lara Lazier <laramglazier@gmail.com>
  Date:   Wed Jul 21 17:26:50 2021 +0200

    target/i386: Added consistency checks for CR4

    All MBZ bits in CR4 must be zero. (APM2 15.5)
    Added reserved bitmask and added checks in both
    helper_vmrun and helper_write_crN.

    Signed-off-by: Lara Lazier <laramglazier@gmail.com>
    Message-Id: <20210721152651.14683-2-laramglazier@gmail.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

In this commit CR4_RESERVED_MASK is missing CR4_LA57_MASK and
two others. Adding this lets Fedora kernels boot once again.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Tested-by: Richard W.M. Jones <rjones@redhat.com>
Message-Id: <20210831175033.175584-1-berrange@redhat.com>
[Removed VMXE/SMXE, matching the commit message. - Paolo]
Fixes: 213ff024a2 ("target/i386: Added consistency checks for CR4", 2021-07-22)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 target/i386/cpu.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 6c50d3ab4f..21b33fbe2e 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -257,6 +257,7 @@ typedef enum X86Seg {
                 | CR4_DE_MASK | CR4_PSE_MASK | CR4_PAE_MASK \
                 | CR4_MCE_MASK | CR4_PGE_MASK | CR4_PCE_MASK \
                 | CR4_OSFXSR_MASK | CR4_OSXMMEXCPT_MASK |CR4_UMIP_MASK \
+                | CR4_LA57_MASK \
                 | CR4_FSGSBASE_MASK | CR4_PCIDE_MASK | CR4_OSXSAVE_MASK \
                 | CR4_SMEP_MASK | CR4_SMAP_MASK | CR4_PKE_MASK | CR4_PKS_MASK))
 
-- 
2.31.1

On Mon, Sep 06, 2021 at 05:26:57PM +0200, Paolo Bonzini wrote:
> From: Daniel P. Berrangé <berrange@redhat.com>
> 
> Booting Fedora kernels with -cpu max hangs very early in boot. Disabling
> the la57 CPUID bit fixes the problem. git bisect traced the regression to
> 
>   commit 213ff024a2f92020290296cb9dc29c2af3d4a221 (HEAD, refs/bisect/bad)
>   Author: Lara Lazier <laramglazier@gmail.com>
>   Date:   Wed Jul 21 17:26:50 2021 +0200
> 
>     target/i386: Added consistency checks for CR4
> 
>     All MBZ bits in CR4 must be zero. (APM2 15.5)
>     Added reserved bitmask and added checks in both
>     helper_vmrun and helper_write_crN.
> 
>     Signed-off-by: Lara Lazier <laramglazier@gmail.com>
>     Message-Id: <20210721152651.14683-2-laramglazier@gmail.com>
>     Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> 
> In this commit CR4_RESERVED_MASK is missing CR4_LA57_MASK and
> two others. Adding this lets Fedora kernels boot once again.
> 
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> Tested-by: Richard W.M. Jones <rjones@redhat.com>

I tested it again and it still works:

$ LIBGUESTFS_BACKEND_SETTINGS=force_tcg LIBGUESTFS_HV=$PWD/qemu-system-x86_64 libguestfs-test-tool
...
===== TEST FINISHED OK =====

(versus without the patch where it appears to hang in very early kernel)

Rich.

> Message-Id: <20210831175033.175584-1-berrange@redhat.com>
> [Removed VMXE/SMXE, matching the commit message. - Paolo]
> Fixes: 213ff024a2 ("target/i386: Added consistency checks for CR4", 2021-07-22)
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  target/i386/cpu.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index 6c50d3ab4f..21b33fbe2e 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -257,6 +257,7 @@ typedef enum X86Seg {
>                  | CR4_DE_MASK | CR4_PSE_MASK | CR4_PAE_MASK \
>                  | CR4_MCE_MASK | CR4_PGE_MASK | CR4_PCE_MASK \
>                  | CR4_OSFXSR_MASK | CR4_OSXMMEXCPT_MASK |CR4_UMIP_MASK \
> +                | CR4_LA57_MASK \
>                  | CR4_FSGSBASE_MASK | CR4_PCIDE_MASK | CR4_OSXSAVE_MASK \
>                  | CR4_SMEP_MASK | CR4_SMAP_MASK | CR4_PKE_MASK | CR4_PKS_MASK))
>  
> -- 
> 2.31.1

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-df lists disk usage of guests without needing to install any
software inside the virtual machine.  Supports Linux and Windows.
http://people.redhat.com/~rjones/virt-df/