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

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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@xxxxxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Coiby Xu <coxu@xxxxxxxxxx>
Cc: Hari Bathini <hbathini@xxxxxxxxxxxxx>
Cc: Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxx>
Signed-off-by: Sourabh Jain <sourabhjain@xxxxxxxxxxxxx>
---
  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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