Re: [PATCH 1/3] kexec_load: Use new kexec flag for hotplug support

[Sourabh Jain <sourabhjain@linux.ibm.com>]

Hello Aditya,


On 28/05/24 17:03, Aditya Gupta wrote:
> Hello sourabh,
>
> On Wed, May 22, 2024 at 06:43:51PM GMT, Sourabh Jain wrote:
>> Kernel commit 79365026f869 (crash: add a new kexec flag for hotplug
>> support) has introduced a new kexec flag to generalize hotplug support.
>> The newly introduced kexec flags for hotplug allow architectures to
>> exclude all the required kexec segments from SHA calculation so that
>> the kernel can update them on hotplug events. This was not possible
>> earlier with the KEXEC_UPDATE_ELFCOREHDR kexec flags since it was added
>> only for the elfcorehdr segment.
>>
>> To enable architectures to control the list of kexec segments to exclude
>> when hotplug support is enabled, add a new architecture-specific
>> function named arch_do_exclude_segment. During the SHA calculation, this
>> function gets called to let the architecture decide whether a specific
>> kexec segment should be considered for SHA calculation or not.
>>
>> Given that the KEXEC_UPDATE_ELFCOREHDR is no longer required and was
>> colliding with the KEXEC_LIVE_UPDATE update flag, it is removed.
>>
>> Cc: Aditya Gupta <adityag@linux.ibm.com>
>> Cc: Baoquan He <bhe@redhat.com>
>> Cc: Coiby Xu <coxu@redhat.com>
>> Cc: Hari Bathini <hbathini@linux.ibm.com>
>> Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
>> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
>> ---
>>   kexec/arch/arm/kexec-arm.c             |  5 +++++
>>   kexec/arch/arm64/kexec-arm64.c         |  4 ++++
>>   kexec/arch/cris/kexec-cris.c           |  4 ++++
>>   kexec/arch/hppa/kexec-hppa.c           |  5 +++++
>>   kexec/arch/i386/kexec-x86.c            |  8 ++++++++
>>   kexec/arch/ia64/kexec-ia64.c           |  4 ++++
>>   kexec/arch/loongarch/kexec-loongarch.c |  5 +++++
>>   kexec/arch/m68k/kexec-m68k.c           |  5 +++++
>>   kexec/arch/mips/kexec-mips.c           |  4 ++++
>>   kexec/arch/ppc/kexec-ppc.c             |  4 ++++
>>   kexec/arch/ppc64/kexec-ppc64.c         |  5 +++++
>>   kexec/arch/s390/kexec-s390.c           |  5 +++++
>>   kexec/arch/sh/kexec-sh.c               |  5 +++++
>>   kexec/arch/x86_64/kexec-x86_64.c       |  5 +++++
>>   kexec/kexec-syscall.h                  |  2 +-
>>   kexec/kexec.c                          | 14 ++++++++------
>>   kexec/kexec.h                          |  2 ++
>>   17 files changed, 79 insertions(+), 7 deletions(-)
>>
>> diff --git a/kexec/arch/arm/kexec-arm.c b/kexec/arch/arm/kexec-arm.c
>> index 49f35b1..34531f9 100644
>> --- a/kexec/arch/arm/kexec-arm.c
>> +++ b/kexec/arch/arm/kexec-arm.c
>> @@ -148,3 +148,8 @@ int have_sysfs_fdt(void)
>>   {
>>   	return !access(SYSFS_FDT, F_OK);
>>   }
>> +
>> +int arch_do_exclude_segment(struct kexec_segment *UNUSED(seg_ptr), struct kexec_info *UNUSED(info))
>> +{
>> +	return 0;
>> +}
>> diff --git a/kexec/arch/arm64/kexec-arm64.c b/kexec/arch/arm64/kexec-arm64.c
>> index 4a67b0d..9d052b0 100644
>> --- a/kexec/arch/arm64/kexec-arm64.c
>> +++ b/kexec/arch/arm64/kexec-arm64.c
>> @@ -1363,3 +1363,7 @@ void arch_reuse_initrd(void)
>>   void arch_update_purgatory(struct kexec_info *UNUSED(info))
>>   {
>>   }
>> +int arch_do_exclude_segment(struct kexec_segment *UNUSED(seg_ptr), struct kexec_info *UNUSED(info))
>> +{
>> +	return 0;
>> +}
>> diff --git a/kexec/arch/cris/kexec-cris.c b/kexec/arch/cris/kexec-cris.c
>> index 3b69709..7f09121 100644
>> --- a/kexec/arch/cris/kexec-cris.c
>> +++ b/kexec/arch/cris/kexec-cris.c
>> @@ -109,3 +109,7 @@ unsigned long add_buffer(struct kexec_info *info, const void *buf,
>>                                       buf_min, buf_max, buf_end, 1);
>>   }
>>   
>> +int arch_do_exclude_segment(struct kexec_segment *UNUSED(seg_ptr), struct kexec_info *UNUSED(info))
>> +{
>> +	return 0;
>> +}
>> diff --git a/kexec/arch/hppa/kexec-hppa.c b/kexec/arch/hppa/kexec-hppa.c
>> index 77c9739..a64dc3d 100644
>> --- a/kexec/arch/hppa/kexec-hppa.c
>> +++ b/kexec/arch/hppa/kexec-hppa.c
>> @@ -146,3 +146,8 @@ unsigned long virt_to_phys(unsigned long addr)
>>   {
>>   	return addr - phys_offset;
>>   }
>> +
>> +int arch_do_exclude_segment(struct kexec_segment *UNUSED(seg_ptr), struct kexec_info *UNUSED(info))
>> +{
>> +	return 0;
>> +}
>> diff --git a/kexec/arch/i386/kexec-x86.c b/kexec/arch/i386/kexec-x86.c
>> index 444cb69..b4947a0 100644
>> --- a/kexec/arch/i386/kexec-x86.c
>> +++ b/kexec/arch/i386/kexec-x86.c
>> @@ -208,3 +208,11 @@ void arch_update_purgatory(struct kexec_info *info)
>>   	elf_rel_set_symbol(&info->rhdr, "panic_kernel",
>>   		&panic_kernel, sizeof(panic_kernel));
>>   }
>> +
>> +int arch_do_exclude_segment(struct kexec_segment *seg_ptr, struct kexec_info *info)
>> +{
>> +	if (info->elfcorehdr == (unsigned long) seg_ptr->mem)
>> +		return 1;
>> +
>> +	return 0;
>> +}
>> diff --git a/kexec/arch/ia64/kexec-ia64.c b/kexec/arch/ia64/kexec-ia64.c
>> index 418d997..8d9c1f3 100644
>> --- a/kexec/arch/ia64/kexec-ia64.c
>> +++ b/kexec/arch/ia64/kexec-ia64.c
>> @@ -245,3 +245,7 @@ void arch_update_purgatory(struct kexec_info *UNUSED(info))
>>   {
>>   }
>>   
>> +int arch_do_exclude_segment(struct kexec_segment *UNUSED(seg_ptr), struct kexec_info *UNUSED(info))
>> +{
>> +	return 0;
>> +}
>> diff --git a/kexec/arch/loongarch/kexec-loongarch.c b/kexec/arch/loongarch/kexec-loongarch.c
>> index 32a42d2..9a50ff6 100644
>> --- a/kexec/arch/loongarch/kexec-loongarch.c
>> +++ b/kexec/arch/loongarch/kexec-loongarch.c
>> @@ -378,3 +378,8 @@ unsigned long add_buffer(struct kexec_info *info, const void *buf,
>>   	return add_buffer_phys_virt(info, buf, bufsz, memsz, buf_align,
>>   				    buf_min, buf_max, buf_end, 1);
>>   }
>> +
>> +int arch_do_exclude_segment(struct kexec_segment *UNUSED(seg_ptr), struct kexec_info *UNUSED(info))
>> +{
>> +	return 0;
>> +}
>> diff --git a/kexec/arch/m68k/kexec-m68k.c b/kexec/arch/m68k/kexec-m68k.c
>> index cb54927..0c7dbaf 100644
>> --- a/kexec/arch/m68k/kexec-m68k.c
>> +++ b/kexec/arch/m68k/kexec-m68k.c
>> @@ -108,3 +108,8 @@ void add_segment(struct kexec_info *info, const void *buf, size_t bufsz,
>>   {
>>   	add_segment_phys_virt(info, buf, bufsz, base, memsz, 1);
>>   }
>> +
>> +int arch_do_exclude_segment(struct kexec_segment *UNUSED(seg_ptr), struct kexec_info *UNUSED(info))
>> +{
>> +	return 0;
>> +}
>> diff --git a/kexec/arch/mips/kexec-mips.c b/kexec/arch/mips/kexec-mips.c
>> index d8cbea8..94224ee 100644
>> --- a/kexec/arch/mips/kexec-mips.c
>> +++ b/kexec/arch/mips/kexec-mips.c
>> @@ -189,3 +189,7 @@ unsigned long add_buffer(struct kexec_info *info, const void *buf,
>>   				    buf_min, buf_max, buf_end, 1);
>>   }
>>   
>> +int arch_do_exclude_segment(const void *UNUSED(seg_ptr), struct kexec_info *UNUSED(info))
>> +{
>> +	return 0;
>> +}
>> diff --git a/kexec/arch/ppc/kexec-ppc.c b/kexec/arch/ppc/kexec-ppc.c
>> index 03bec36..c8af870 100644
>> --- a/kexec/arch/ppc/kexec-ppc.c
>> +++ b/kexec/arch/ppc/kexec-ppc.c
>> @@ -966,3 +966,7 @@ void arch_update_purgatory(struct kexec_info *UNUSED(info))
>>   {
>>   }
>>   
>> +int arch_do_exclude_segment(struct kexec_segment *UNUSED(seg_ptr), struct kexec_info *UNUSED(info))
>> +{
>> +	return 0;
>> +}
>> diff --git a/kexec/arch/ppc64/kexec-ppc64.c b/kexec/arch/ppc64/kexec-ppc64.c
>> index bd5274c..fb27b6b 100644
>> --- a/kexec/arch/ppc64/kexec-ppc64.c
>> +++ b/kexec/arch/ppc64/kexec-ppc64.c
>> @@ -967,3 +967,8 @@ int arch_compat_trampoline(struct kexec_info *UNUSED(info))
>>   void arch_update_purgatory(struct kexec_info *UNUSED(info))
>>   {
>>   }
>> +
>> +int arch_do_exclude_segment(struct kexec_segment *UNUSED(seg_ptr), struct kexec_info *UNUSED(info))
>> +{
>> +	return 0;
>> +}
>> diff --git a/kexec/arch/s390/kexec-s390.c b/kexec/arch/s390/kexec-s390.c
>> index 33ba6b9..0561ee7 100644
>> --- a/kexec/arch/s390/kexec-s390.c
>> +++ b/kexec/arch/s390/kexec-s390.c
>> @@ -267,3 +267,8 @@ int get_crash_kernel_load_range(uint64_t *start, uint64_t *end)
>>   {
>>   	return parse_iomem_single("Crash kernel\n", start, end);
>>   }
>> +
>> +int arch_do_exclude_segment(struct kexec_segment *UNUSED(seg_ptr), struct kexec_info *UNUSED(info))
>> +{
>> +	return 0;
>> +}
>> diff --git a/kexec/arch/sh/kexec-sh.c b/kexec/arch/sh/kexec-sh.c
>> index ce341c8..f84c40c 100644
>> --- a/kexec/arch/sh/kexec-sh.c
>> +++ b/kexec/arch/sh/kexec-sh.c
>> @@ -257,3 +257,8 @@ unsigned long add_buffer(struct kexec_info *info, const void *buf,
>>   	return add_buffer_phys_virt(info, buf, bufsz, memsz, buf_align,
>>   				    buf_min, buf_max, buf_end, 1);
>>   }
>> +
>> +int arch_do_exclude_segment(struct kexec_segment *UNUSED(seg_ptr), struct kexec_info *UNUSED(info))
>> +{
>> +	return 0;
>> +}
>> diff --git a/kexec/arch/x86_64/kexec-x86_64.c b/kexec/arch/x86_64/kexec-x86_64.c
>> index ffd84f0..42af90a 100644
>> --- a/kexec/arch/x86_64/kexec-x86_64.c
>> +++ b/kexec/arch/x86_64/kexec-x86_64.c
>> @@ -188,3 +188,8 @@ void arch_update_purgatory(struct kexec_info *info)
>>   	elf_rel_set_symbol(&info->rhdr, "panic_kernel",
>>   				&panic_kernel, sizeof(panic_kernel));
>>   }
>> +
>> +int arch_do_exclude_segment(struct kexec_segment *UNUSED(seg_ptr), struct kexec_info *UNUSED(info))
>> +{
>> +	return 0;
>> +}
> Should all arch_do_exclude_segment return 1 for elfcorehdr ? Please
> refer my below comment.

No they shouldn't until they have CRASH_HTOPLUG support in the kernel.


>
>> diff --git a/kexec/kexec-syscall.h b/kexec/kexec-syscall.h
>> index 73e5254..4675c46 100644
>> --- a/kexec/kexec-syscall.h
>> +++ b/kexec/kexec-syscall.h
>> @@ -112,7 +112,7 @@ static inline long kexec_file_load(int kernel_fd, int initrd_fd,
>>   
>>   #define KEXEC_ON_CRASH		0x00000001
>>   #define KEXEC_PRESERVE_CONTEXT	0x00000002
>> -#define KEXEC_UPDATE_ELFCOREHDR	0x00000004
>> +#define KEXEC_CRASH_HOTPLUG_SUPPORT	0x00000008
>>   #define KEXEC_ARCH_MASK		0xffff0000
>>   
>>   /* Flags for kexec file based system call */
>> diff --git a/kexec/kexec.c b/kexec/kexec.c
>> index 222f79e..034cea6 100644
>> --- a/kexec/kexec.c
>> +++ b/kexec/kexec.c
>> @@ -701,10 +701,13 @@ static void update_purgatory(struct kexec_info *info)
>>   			continue;
>>   		}
>>   
>> -		/* Don't include elfcorehdr in the checksum, if hotplug
>> -		 * support enabled.
>> +		/*
>> +		 * Let architecture decide which segments to exclude from checksum
>> +		 * if hotplug support is enabled.
>>   		 */
>> -		if (do_hotplug && (info->segment[i].mem == (void *)info->elfcorehdr)) {
>> +		if (do_hotplug && arch_do_exclude_segment(&info->segment[i], info)) {
>> +			dbgprintf("Skipping segment mem: 0x%lx from SHA calculation\n",
>> +				  (unsigned long)info->segment[i].mem);
>>   			continue;
>>   		}
> Current behaviour seems to skip elfcorehdr segment in all architectures.
>
> But now as all architectures are returning 0 in arch_do_exclude_segment,
> will elfcorehdr still be skipped ?

Skipping elfcorehdr for architectures that don't support CRASH_HOTPLUG 
is, I think, incorrect.
Therefore, I believe the proposed approach in this patch, which asks the 
architecture which
segments to exclude, is better.

> Rest all looks good to me.

Thanks for the review.


- Sourabh Jain

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