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Date:   Wed, 27 Jan 2021 10:42:30 -0600
From:   Tyler Hicks <tyhicks@linux.microsoft.com>
To:     Pavel Tatashin <pasha.tatashin@soleen.com>
Cc:     jmorris@namei.org, sashal@kernel.org, ebiederm@xmission.com,
        kexec@lists.infradead.org, linux-kernel@vger.kernel.org,
        corbet@lwn.net, catalin.marinas@arm.com, will@kernel.org,
        linux-arm-kernel@lists.infradead.org, maz@kernel.org,
        james.morse@arm.com, vladimir.murzin@arm.com,
        matthias.bgg@gmail.com, linux-mm@kvack.org, mark.rutland@arm.com,
        steve.capper@arm.com, rfontana@redhat.com, tglx@linutronix.de,
        selindag@gmail.com
Subject: Re: [PATCH v10 16/18] arm64: kexec: configure trans_pgd page table
 for kexec
Message-ID: <20210127164230.GA584465@sequoia>
References: <20210125191923.1060122-1-pasha.tatashin@soleen.com>
 <20210125191923.1060122-17-pasha.tatashin@soleen.com>
 <d5b91732-1985-4d90-89a1-4873deaa5592@soleen.com>
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On 2021-01-25 19:21:22, Pavel Tatashin wrote:
> I forgot to make changes to arch/arm64/Kconfig. The correct patch is
> below.
> 
> ---
> 
> From a2bc374320d7c7efd3c40644ad3d6d59a024b301 Mon Sep 17 00:00:00 2001
> From: Pavel Tatashin <pasha.tatashin@soleen.com>
> Date: Mon, 29 Jul 2019 21:24:25 -0400
> Subject: [PATCH v10 16/18] arm64: kexec: configure trans_pgd page table for
>  kexec
> 
> Configure a page table located in kexec-safe memory that has
> the following mappings:
> 
> 1. identity mapping for text of relocation function with executable
>    permission.
> 2. va mappings for all source ranges
> 3. va mappings for all destination ranges.
> 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
> ---
>  arch/arm64/Kconfig                |  2 +-
>  arch/arm64/include/asm/kexec.h    | 12 ++++
>  arch/arm64/kernel/asm-offsets.c   |  6 ++
>  arch/arm64/kernel/machine_kexec.c | 91 ++++++++++++++++++++++++++++++-
>  4 files changed, 109 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index fc0ed9d6e011..440abd0c0ee1 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1134,7 +1134,7 @@ config CRASH_DUMP
>  
>  config TRANS_TABLE
>  	def_bool y
> -	depends on HIBERNATION
> +	depends on HIBERNATION || KEXEC_CORE
>  
>  config XEN_DOM0
>  	def_bool y
> diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
> index b96d8a6aac80..049cde429b1b 100644
> --- a/arch/arm64/include/asm/kexec.h
> +++ b/arch/arm64/include/asm/kexec.h
> @@ -105,6 +105,12 @@ extern const char arm64_kexec_el2_vectors[];
>   * el2_vector	If present means that relocation routine will go to EL1
>   *		from EL2 to do the copy, and then back to EL2 to do the jump
>   *		to new world.
> + * trans_ttbr0	idmap for relocation function and its argument
> + * trans_ttbr1	map for source/destination addresses.
> + * trans_t0sz	t0sz for idmap page in trans_ttbr0
> + * src_addr	start address for source pages.
> + * dst_addr	start address for destination pages.
> + * copy_len	Number of bytes that need to be copied
>   */
>  struct kern_reloc_arg {
>  	phys_addr_t head;
> @@ -114,6 +120,12 @@ struct kern_reloc_arg {
>  	phys_addr_t kern_arg2;
>  	phys_addr_t kern_arg3;
>  	phys_addr_t el2_vector;
> +	phys_addr_t trans_ttbr0;
> +	phys_addr_t trans_ttbr1;
> +	unsigned long trans_t0sz;
> +	unsigned long src_addr;
> +	unsigned long dst_addr;
> +	unsigned long copy_len;
>  };
>  
>  #define ARCH_HAS_KIMAGE_ARCH
> diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
> index 8a9475be1b62..06278611451d 100644
> --- a/arch/arm64/kernel/asm-offsets.c
> +++ b/arch/arm64/kernel/asm-offsets.c
> @@ -160,6 +160,12 @@ int main(void)
>    DEFINE(KEXEC_KRELOC_KERN_ARG2,	offsetof(struct kern_reloc_arg, kern_arg2));
>    DEFINE(KEXEC_KRELOC_KERN_ARG3,	offsetof(struct kern_reloc_arg, kern_arg3));
>    DEFINE(KEXEC_KRELOC_EL2_VECTOR,	offsetof(struct kern_reloc_arg, el2_vector));
> +  DEFINE(KEXEC_KRELOC_TRANS_TTBR0,	offsetof(struct kern_reloc_arg, trans_ttbr0));
> +  DEFINE(KEXEC_KRELOC_TRANS_TTBR1,	offsetof(struct kern_reloc_arg, trans_ttbr1));
> +  DEFINE(KEXEC_KRELOC_TRANS_T0SZ,	offsetof(struct kern_reloc_arg, trans_t0sz));
> +  DEFINE(KEXEC_KRELOC_SRC_ADDR,	offsetof(struct kern_reloc_arg, src_addr));
> +  DEFINE(KEXEC_KRELOC_DST_ADDR,	offsetof(struct kern_reloc_arg, dst_addr));
> +  DEFINE(KEXEC_KRELOC_COPY_LEN,	offsetof(struct kern_reloc_arg, copy_len));
>  #endif
>    return 0;
>  }
> diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
> index 41d1e3ca13f8..dc1b7e5a54fb 100644
> --- a/arch/arm64/kernel/machine_kexec.c
> +++ b/arch/arm64/kernel/machine_kexec.c
> @@ -21,6 +21,7 @@
>  #include <asm/mmu_context.h>
>  #include <asm/page.h>
>  #include <asm/sections.h>
> +#include <asm/trans_pgd.h>
>  
>  #include "cpu-reset.h"
>  
> @@ -71,11 +72,91 @@ static void *kexec_page_alloc(void *arg)
>  	return page_address(page);
>  }
>  
> +/*
> + * Map source segments starting from src_va, and map destination
> + * segments starting from dst_va, and return size of copy in
> + * *copy_len argument.
> + * Relocation function essentially needs to do:
> + * memcpy(dst_va, src_va, copy_len);
> + */
> +static int map_segments(struct kimage *kimage, pgd_t *pgdp,
> +			struct trans_pgd_info *info,
> +			unsigned long src_va,
> +			unsigned long dst_va,
> +			unsigned long *copy_len)
> +{
> +	unsigned long *ptr = 0;
> +	unsigned long dest = 0;
> +	unsigned long len = 0;
> +	unsigned long entry, addr;
> +	int rc;
> +
> +	for (entry = kimage->head; !(entry & IND_DONE); entry = *ptr++) {
> +		addr = entry & PAGE_MASK;
> +
> +		switch (entry & IND_FLAGS) {
> +		case IND_DESTINATION:
> +			dest = addr;
> +			break;
> +		case IND_INDIRECTION:
> +			ptr = __va(addr);
> +			if (rc)

We're checking a potentially uninitialized value here. I think this
whole "if (rc) return rc;" conditional can go away.

Tyler

> +				return rc;
> +			break;
> +		case IND_SOURCE:
> +			rc = trans_pgd_map_page(info, pgdp, __va(addr),
> +						src_va, PAGE_KERNEL);
> +			if (rc)
> +				return rc;
> +			rc = trans_pgd_map_page(info, pgdp, __va(dest),
> +						dst_va, PAGE_KERNEL);
> +			if (rc)
> +				return rc;
> +			dest += PAGE_SIZE;
> +			src_va += PAGE_SIZE;
> +			dst_va += PAGE_SIZE;
> +			len += PAGE_SIZE;
> +		}
> +	}
> +	*copy_len = len;
> +
> +	return 0;
> +}
> +
> +static int mmu_relocate_setup(struct kimage *kimage, void *reloc_code,
> +			      struct kern_reloc_arg *kern_reloc_arg)
> +{
> +	struct trans_pgd_info info = {
> +		.trans_alloc_page	= kexec_page_alloc,
> +		.trans_alloc_arg	= kimage,
> +	};
> +	pgd_t *trans_pgd = kexec_page_alloc(kimage);
> +	int rc;
> +
> +	if (!trans_pgd)
> +		return -ENOMEM;
> +
> +	/* idmap relocation function */
> +	rc = trans_pgd_idmap_page(&info, &kern_reloc_arg->trans_ttbr0,
> +				  &kern_reloc_arg->trans_t0sz, reloc_code);
> +	if (rc)
> +		return rc;
> +
> +	kern_reloc_arg->src_addr = _PAGE_OFFSET(VA_BITS_MIN);
> +	kern_reloc_arg->dst_addr = _PAGE_OFFSET(VA_BITS_MIN - 1);
> +	kern_reloc_arg->trans_ttbr1 = phys_to_ttbr(__pa(trans_pgd));
> +
> +	rc = map_segments(kimage, trans_pgd, &info, kern_reloc_arg->src_addr,
> +			  kern_reloc_arg->dst_addr, &kern_reloc_arg->copy_len);
> +	return rc;
> +}
> +
>  int machine_kexec_post_load(struct kimage *kimage)
>  {
>  	void *reloc_code = page_to_virt(kimage->control_code_page);
>  	struct kern_reloc_arg *kern_reloc_arg = kexec_page_alloc(kimage);
>  	long func_offset, vector_offset, reloc_size;
> +	int rc = 0;
>  
>  	if (!kern_reloc_arg)
>  		return -ENOMEM;
> @@ -95,6 +176,14 @@ int machine_kexec_post_load(struct kimage *kimage)
>  	if (is_hyp_mode_available() && !is_kernel_in_hyp_mode())
>  		kern_reloc_arg->el2_vector = __pa(reloc_code) + vector_offset;
>  
> +	/*
> +	 * If relocation is not needed, we do not need to enable MMU in
> +	 * relocation routine, therefore do not create page tables for
> +	 * scenarios such as crash kernel
> +	 */
> +	if (!(kimage->head & IND_DONE))
> +		rc = mmu_relocate_setup(kimage, reloc_code, kern_reloc_arg);
> +
>  	kexec_image_info(kimage);
>  
>  	/* Flush the reloc_code in preparation for its execution. */
> @@ -103,7 +192,7 @@ int machine_kexec_post_load(struct kimage *kimage)
>  			   reloc_size);
>  	__flush_dcache_area(kern_reloc_arg, sizeof(struct kern_reloc_arg));
>  
> -	return 0;
> +	return rc;
>  }
>  
>  /**
> -- 
> 2.25.1
>