Re: [PATCH v3 3/3] x86/PVH: Support relocatable dom0 kernels

From: Jan Beulich <jbeulich@suse.com>
To: Jason Andryuk <jason.andryuk@amd.com>
Cc: "Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>, "Wei Liu" <wl@xen.org>,
	"George Dunlap" <george.dunlap@citrix.com>,
	"Julien Grall" <julien@xen.org>,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	xen-devel@lists.xenproject.org
Subject: Re: [PATCH v3 3/3] x86/PVH: Support relocatable dom0 kernels
Date: Mon, 25 Mar 2024 08:46:01 +0100	[thread overview]
Message-ID: <b0e4d3e0-f760-4ba2-a90b-f8c5ddb676ad@suse.com> (raw)
In-Reply-To: <63cad597-b48f-43df-8d53-0ee8c1aa744d@amd.com>

On 22.03.2024 15:24, Jason Andryuk wrote:
> On 2024-03-21 09:45, Jason Andryuk wrote:
>> On 2024-03-20 10:39, Jan Beulich wrote:
>>> On 19.03.2024 21:58, Jason Andryuk wrote:
> 
>>>> @@ -536,6 +565,10 @@ elf_errorstatus elf_xen_parse(struct elf_binary 
>>>> *elf,
>>>>       parms->p2m_base = UNSET_ADDR;
>>>>       parms->elf_paddr_offset = UNSET_ADDR;
>>>>       parms->phys_entry = UNSET_ADDR32;
>>>> +    parms->phys_min = 0;
>>>> +    parms->phys_max = 0xffffffff;
>>>> +    parms->phys_align = 0x200000;
>>>
>>> I think this wants to be MB(2) (requiring a pre-patch to centralize MB()
>>> in the tool stack to tools/include/xen-tools/common-macros.h). And I
>>> further think this needs to be an arch-specific constant, even if right
>>> now the note is expected to be present only for x86. Which then also
>>> needs saying ...
> 
> Are you thinking something like the following in libelf-dominfo.c:
> 
> #define X86_PHYS_ALIGN_DEFAULT MB(2)
> #define X86_PHYS_MAX_DEFAULT (GB(4) - 1)
> 
> and setting as:
> parms->phys_max = X86_PHYS_MAX_DEFAULT;
> parms->phys_align = X86_PHYS_ALIGN_DEFAULT;
> 
> libelf is arch neutral, so there isn't a natural place to introduce 
> arch-specific defines.  Or were you looking for each arch to set it?  We 
> only care about x86 right now, so we can do something like:
> 
> #if x86
> #define ARCH_PHYS_MAX_DEFAULT   (GB(4) - 1)
> #define ARCH_PHYS_ALIGN_DEFAULT MB(2)
> #else
> #define ARCH_PHYS_MAX_DEFAULT   0
> #define ARCH_PHYS_ALIGN_DEFAULT 0
> #endif

More like the latter. The former only if the phys_* fields themselves were
to also become x86-only.

As you say, libelf in its present shape doesn't easily lend itself to such
arch-specifics.

Jan