linux-kernel - Re: [PATCH 3/3] x86/64/kexec: Rewrite init_transition_pgtable() with kernel_ident_mapping

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Message-ID: <cd655676d5e81ca9b1de0a66f5f5c719ef816c89.camel@intel.com>
Date: Wed, 3 Jul 2024 11:06:21 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "luto@...nel.org" <luto@...nel.org>, "rafael@...nel.org"
	<rafael@...nel.org>, "dave.hansen@...ux.intel.com"
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	<hpa@...or.com>, "mingo@...hat.com" <mingo@...hat.com>,
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CC: "thomas.lendacky@....com" <thomas.lendacky@....com>,
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	"tzimmermann@...e.de" <tzimmermann@...e.de>
Subject: Re: [PATCH 3/3] x86/64/kexec: Rewrite init_transition_pgtable() with
 kernel_ident_mapping_init()

On Mon, 2024-07-01 at 15:43 +0300, Kirill A. Shutemov wrote:
> init_transition_pgtable() setups transitional page tables. Rewrite it
> using kernel_ident_mapping_init() to avoid code duplication.

setups -> sets up

> 
> struct kimage_arch changed to track allocated page tables as a list, not
> linking them to specific page table levels.

This doesn't look like imperative mode.  Perhaps change to:

  Change struct kimage_arch to track ...

[...]


>  static int init_transition_pgtable(struct kimage *image, pgd_t *pgd)
>  {
> -	pgprot_t prot = PAGE_KERNEL_EXEC_NOENC;
> -	unsigned long vaddr, paddr;
> -	int result = -ENOMEM;
> -	p4d_t *p4d;
> -	pud_t *pud;
> -	pmd_t *pmd;
> -	pte_t *pte;
> +	struct x86_mapping_info info = {
> +		.alloc_pgt_page	= alloc_transition_pgt_page,
> +		.context	= image,
> +		.page_flag	= __PAGE_KERNEL_LARGE_EXEC,
> +		.kernpg_flag	= _KERNPG_TABLE_NOENC,
> +		.offset = __START_KERNEL_map - phys_base,
> +	};
> +	unsigned long mstart = PAGE_ALIGN_DOWN(__pa(relocate_kernel));
> +	unsigned long mend = mstart + PAGE_SIZE;
>  
> -	vaddr = (unsigned long)relocate_kernel;
> -	paddr = __pa(page_address(image->control_code_page)+PAGE_SIZE);

Perhaps I am missing something, but this seems a functional change to me.

IIUC the page after image->control_code_page is allocated when loading the
kexec kernel image.  It is a different page from the page where the
relocate_kernel code resides in.

The old code maps relocate_kernel kernel VA to the page after the
control_code_page.  Later in machine_kexec(), the relocate_kernel code is
copied to that page so the mapping can work for that:

	control_page = page_address(image->control_code_page) + PAGE_SIZE;
	__memcpy(control_page, relocate_kernel,
KEXEC_CONTROL_CODE_MAX_SIZE);

The new code in this patch, however, seems just maps the relocate_kernel VA
to the PA of the relocate_kernel, which should be different from the old
mapping.