linux-kernel - Re: [PATCH] xen/x86: obtain upper 32 bits of video frame buffer address for Dom0

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Date:   Tue, 4 Jan 2022 17:54:59 +0100
From:   Jan Beulich <jbeulich@...e.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH] xen/x86: obtain upper 32 bits of video frame buffer
 address for Dom0

On 04.01.2022 17:50, Boris Ostrovsky wrote:
> 
> On 1/4/22 3:46 AM, Jan Beulich wrote:
>> The hypervisor has been supplying this information for a couple of major
>> releases. Make use of it. The need to set a flag in the capabilities
>> field also points out that the prior setting of that field from the
>> hypervisor interface's gbl_caps one was wrong, so that code gets deleted
>> (there's also no equivalent of this in native boot code).
>>
>> Signed-off-by: Jan Beulich <jbeulich@...e.com>
>>
>> --- a/arch/x86/xen/vga.c
>> +++ b/arch/x86/xen/vga.c
>> @@ -63,13 +63,17 @@ void __init xen_init_vga(const struct do
>>   		}
>>   
>>   		if (size >= offsetof(struct dom0_vga_console_info,
>> -				     u.vesa_lfb.gbl_caps)
>> -		    + sizeof(info->u.vesa_lfb.gbl_caps))
>> -			screen_info->capabilities = info->u.vesa_lfb.gbl_caps;
>> -		if (size >= offsetof(struct dom0_vga_console_info,
>>   				     u.vesa_lfb.mode_attrs)
>>   		    + sizeof(info->u.vesa_lfb.mode_attrs))
> 
> 
> Do we still need this test? All 4.0+ hypervisors will have mode_attrs.

Perhaps this could also be dropped, but unlike the capabilities part
I'd view this as an unrelated change. Furthermore even a new hypervisor
would be free to omit the field, provided it also sets size low enough.

Jan