linux-kernel - Re: [PATCH v3 1/2] x86/mm: Handle alloc failure in phys_*

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Message-ID: <22cd0fa8-d14d-4d37-a6a1-5e6827d6182b@intel.com>
Date: Tue, 10 Jun 2025 07:55:36 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Em Sharnoff <sharnoff@...n.tech>, linux-kernel@...r.kernel.org,
 x86@...nel.org, linux-mm@...ck.org
Cc: Ingo Molnar <mingo@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski
 <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
 "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
 Oleg Vasilev <oleg@...n.tech>, Arthur Petukhovsky <arthur@...n.tech>,
 Stefan Radig <stefan@...n.tech>, Misha Sakhnov <misha@...n.tech>
Subject: Re: [PATCH v3 1/2] x86/mm: Handle alloc failure in phys_*_init()

On 6/10/25 03:16, Em Sharnoff wrote:
> +		if (!pmd)
> +			return (unsigned long)ERR_PTR(-ENOMEM);

All of this casting isn't great to look at. Just about every line of
code that this patch touches also introduces has a cast.

Could you please find a way to reduce the number of casts?

> +		/*
> +		 * We might have IS_ERR(paddr_last) if allocation failed, but we should
> +		 * still update pud before bailing, so that subsequent retries can pick
> +		 * up on progress (here and in phys_pmd_init) without leaking pmd.
> +		 */

Please write everything in imperative voice. No "we's", please.

> -	for (i = 0; i < nr_range; i++)
> +	for (i = 0; i < nr_range; i++) {
>  		ret = kernel_physical_mapping_init(mr[i].start, mr[i].end,
>  						   mr[i].page_size_mask,
>  						   prot);
> +		if (IS_ERR((void *)ret))
> +			return ret;
> +	}

Are there any _actual_ users of 'paddr_last'? I see a lot of setting it
and passing it around, but I _think_ this is the only place it actually
gets used. Here, the fact that it's an address doesn't even matter.