linux-kernel - Re: [PATCH v6 11/14] x86: add KHO support

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Message-ID: <e90b81a4-a912-4174-b6e9-46a6ddd92ee3@intel.com>
Date: Tue, 29 Apr 2025 09:05:02 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: Changyuan Lyu <changyuanl@...gle.com>, linux-kernel@...r.kernel.org,
 akpm@...ux-foundation.org, anthony.yznaga@...cle.com, arnd@...db.de,
 ashish.kalra@....com, benh@...nel.crashing.org, bp@...en8.de,
 catalin.marinas@....com, corbet@....net, dave.hansen@...ux.intel.com,
 devicetree@...r.kernel.org, dwmw2@...radead.org, ebiederm@...ssion.com,
 graf@...zon.com, hpa@...or.com, jgowans@...zon.com,
 kexec@...ts.infradead.org, krzk@...nel.org,
 linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
 linux-mm@...ck.org, luto@...nel.org, mark.rutland@....com, mingo@...hat.com,
 pasha.tatashin@...een.com, pbonzini@...hat.com, peterz@...radead.org,
 ptyadav@...zon.de, robh@...nel.org, rostedt@...dmis.org,
 saravanak@...gle.com, skinsburskii@...ux.microsoft.com, tglx@...utronix.de,
 thomas.lendacky@....com, will@...nel.org, x86@...nel.org
Subject: Re: [PATCH v6 11/14] x86: add KHO support

On 4/29/25 08:53, Mike Rapoport wrote:
> On Mon, Apr 28, 2025 at 03:05:55PM -0700, Dave Hansen wrote:
>> On 4/10/25 22:37, Changyuan Lyu wrote:
>>> From: Alexander Graf <graf@...zon.com>
>>>
>>> +#ifdef CONFIG_KEXEC_HANDOVER
>>> +static bool process_kho_entries(unsigned long minimum, unsigned long image_size)
>>> +{
>>> +	struct kho_scratch *kho_scratch;
>>> +	struct setup_data *ptr;
>>> +	int i, nr_areas = 0;
>>
>> Do these really need actual #ifdefs or will a nice IS_ENABLED() check
>> work instead?
>>
>>> +	ptr = (struct setup_data *)(unsigned long)boot_params_ptr->hdr.setup_data;
>>
>> What's with the double cast?
> 
> The double cast is required for this to be compiled on 32 bits (just like
> in mem_avoid_overlap). The setup_data is all u64 and to cast it to a
> pointer on 32 bit it has to go via unsigned long.

Let's just make KHO depend on 64BIT, at least on x86.

>>> diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c
>>> index 68530fad05f74..518635cc0876c 100644
>>> --- a/arch/x86/kernel/kexec-bzimage64.c
>>> +++ b/arch/x86/kernel/kexec-bzimage64.c
>>> @@ -233,6 +233,31 @@ setup_ima_state(const struct kimage *image, struct boot_params *params,
>>>  #endif /* CONFIG_IMA_KEXEC */
>>>  }
>>>  
>>> +static void setup_kho(const struct kimage *image, struct boot_params *params,
>>> +		      unsigned long params_load_addr,
>>> +		      unsigned int setup_data_offset)
>>> +{
>>> +#ifdef CONFIG_KEXEC_HANDOVER
>>
>> Can this #ifdef be replaced with IS_ENABLED()?
> 
> The KHO structures in kexec image are under #ifdef, so it won't compile
> with IS_ENABLED().

They shouldn't be. Define them unconditionally, please.

...
>> Please axe the #ifdef in the .c file if at all possible, just like the
>> others.
> 
> This one follows IMA, but it's easy to make it IS_ENABLED(). It's really up
> to x86 folks preference.

Last I checked, I'm listed under the big M: for "X86 ARCHITECTURE". ;)