Re: [PATCH v2] xen/x86: Check supported features even for PVH dom0

[Jan Beulich <jbeulich@xxxxxxxx>]

On 03.04.2026 12:11, Roger Pau Monné wrote:
> On Thu, Apr 02, 2026 at 04:55:10PM +0100, Frediano Ziglio wrote:
>> The supported features ELF notes was tested only if the dom0 was
>> PV. Factor out a function to check ELF notes and reuse it even
>> for PVH.
>>
>> Signed-off-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>
>> --
>> Changes since v1:
>> - fix typo in title;
>> - fix minor formatting issue;
>> - use is_hardware_domain instead of checking is_pv_shim;
>> - reduce indentation returning earlier;
>> - return error instead of jumping to cleanup code.
>> ---
>>  xen/arch/x86/dom0_build.c             | 14 ++++++++++++++
>>  xen/arch/x86/hvm/dom0_build.c         |  3 +++
>>  xen/arch/x86/include/asm/dom0_build.h |  2 ++
>>  xen/arch/x86/pv/dom0_build.c          | 10 ++--------
>>  4 files changed, 21 insertions(+), 8 deletions(-)
>>
>> diff --git a/xen/arch/x86/dom0_build.c b/xen/arch/x86/dom0_build.c
>> index 864dd9e53e..a33ce77321 100644
>> --- a/xen/arch/x86/dom0_build.c
>> +++ b/xen/arch/x86/dom0_build.c
>> @@ -320,6 +320,20 @@ unsigned long __init dom0_paging_pages(const struct 
>> domain *d,
>>      return DIV_ROUND_UP(memkb, 1024) << (20 - PAGE_SHIFT);
>>  }
>>  
>> +int __init dom0_check_parms(
>> +    struct domain *d, const struct elf_dom_parms *parms)
> 
> d should be const also.
> 
>> +{
>> +    if ( parms->elf_notes[XEN_ELFNOTE_SUPPORTED_FEATURES].type == 
>> XEN_ENT_NONE )
>> +        return 0;
>> +
>> +    if ( is_hardware_domain(d) && !test_bit(XENFEAT_dom0, 
>> parms->f_supported) )
>> +    {
>> +        printk("Kernel does not support Dom0 operation\n");
>> +        return -EINVAL;
>> +    }
>> +
>> +    return 0;
>> +}
>>  
>>  /*
>>   * If allocation isn't specified, reserve 1/16th of available memory for
>> diff --git a/xen/arch/x86/hvm/dom0_build.c b/xen/arch/x86/hvm/dom0_build.c
>> index d69a83b089..f95a00acfd 100644
>> --- a/xen/arch/x86/hvm/dom0_build.c
>> +++ b/xen/arch/x86/hvm/dom0_build.c
>> @@ -699,6 +699,9 @@ static int __init pvh_load_kernel(
>>      if ( !check_and_adjust_load_address(d, &elf, &parms) )
>>          return -ENOSPC;
>>  
>> +    if ( (rc = dom0_check_parms(d, &parms)) != 0 )
>> +        return rc;
> 
> I would do the check ahead of check_and_adjust_load_address(), as then
> we could avoid the load address adjustment if we detect earlier than
> the dom0 feature is not present.  But that's just my taste.

+1, perhaps even yet a few more lines further up.

Jan