Re: [PATCH v2 1/2] powerpc/fadump: allocate memory for additional parameters early

[Sourabh Jain]

Hello Ritesh

On 12/11/24 12:33, Ritesh Harjani (IBM) wrote:
Sourabh Jain <sourabhj...@linux.ibm.com> writes:
From: Hari Bathini <hbath...@linux.ibm.com>

Memory for passing additional parameters to fadump capture kernel
is allocated during subsys_initcall level, using memblock. But
as slab is already available by this time, allocation happens via
the buddy allocator. This may work for radix MMU but is likely to
fail in most cases for hash MMU as hash MMU needs this memory in
the first memory block for it to be accessible in real mode in the
capture kernel (second boot). So, allocate memory for additional
parameters area as soon as MMU mode is obvious.
But looks like this was only caught due to the WARN_ON_ONCE emitted from
mm/memblock.c which detected accidental use of memblock APIs when slab is
available. That begs a question on why didn't we see the issue on Hash?

We do see the issues with the hash as mentioned in the commit message.

Are we not using the "param_area_supported" feature that often is it?

Yes, because it is a relatively new feature, and the userspace changes 
required to
make use of this feature using kdump service are not part of the distro yet.



Fixes: 683eab94da75 ("powerpc/fadump: setup additional parameters for dump capture 
kernel")
Reported-by: Venkat Rao Bagalkote <venka...@linux.vnet.ibm.com>
Closes: 
https://lore.kernel.org/lkml/a70e4064-a040-447b-8556-1fd02f193...@linux.vnet.ibm.com/T/#u
Cc: Mahesh Salgaonkar <mah...@linux.ibm.com>
Cc: Michael Ellerman <m...@ellerman.id.au>
Signed-off-by: Hari Bathini <hbath...@linux.ibm.com>
Signed-off-by: Sourabh Jain <sourabhj...@linux.ibm.com>
---

Changelog:

Since v1: 
https://lore.kernel.org/all/20241104083528.99520-1-sourabhj...@linux.ibm.com/
   - Drop extern keyword from fadump_setup_param_area function declaration
   - Don't use __va() while resetting param memory area

---
  arch/powerpc/include/asm/fadump.h |  2 ++
  arch/powerpc/kernel/fadump.c      | 15 ++++++++++-----
  arch/powerpc/kernel/prom.c        |  3 +++
  3 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/include/asm/fadump.h 
b/arch/powerpc/include/asm/fadump.h
index ef40c9b6972a..7b3473e05273 100644
--- a/arch/powerpc/include/asm/fadump.h
+++ b/arch/powerpc/include/asm/fadump.h
@@ -19,6 +19,7 @@ extern int is_fadump_active(void);
  extern int should_fadump_crash(void);
  extern void crash_fadump(struct pt_regs *, const char *);
  extern void fadump_cleanup(void);
+void fadump_setup_param_area(void);
  extern void fadump_append_bootargs(void);
  
  #else	/* CONFIG_FA_DUMP */
@@ -26,6 +27,7 @@ static inline int is_fadump_active(void) { return 0; }
  static inline int should_fadump_crash(void) { return 0; }
  static inline void crash_fadump(struct pt_regs *regs, const char *str) { }
  static inline void fadump_cleanup(void) { }
+static inline void fadump_setup_param_area(void) { }
  static inline void fadump_append_bootargs(void) { }
  #endif /* !CONFIG_FA_DUMP */
  
diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
index a612e7513a4f..3a2863307863 100644
--- a/arch/powerpc/kernel/fadump.c
+++ b/arch/powerpc/kernel/fadump.c
@@ -1586,6 +1586,12 @@ static void __init fadump_init_files(void)
                return;
        }
  
+	if (fw_dump.param_area) {
+               rc = sysfs_create_file(fadump_kobj, &bootargs_append_attr.attr);
+               if (rc)
+                       pr_err("unable to create bootargs_append sysfs file 
(%d)\n", rc);
+       }
+
        debugfs_create_file("fadump_region", 0444, arch_debugfs_dir, NULL,
                            &fadump_region_fops);
  
@@ -1740,7 +1746,7 @@ static void __init fadump_process(void)
   * Reserve memory to store additional parameters to be passed
   * for fadump/capture kernel.
   */
-static void __init fadump_setup_param_area(void)
+void __init fadump_setup_param_area(void)
  {
        phys_addr_t range_start, range_end;
  
@@ -1748,7 +1754,7 @@ static void __init fadump_setup_param_area(void)
                return;
  
  	/* This memory can't be used by PFW or bootloader as it is shared across kernels */
-       if (radix_enabled()) {
+       if (early_radix_enabled()) {
                /*
                 * Anywhere in the upper half should be good enough as all 
memory
                 * is accessible in real mode.
@@ -1776,12 +1782,12 @@ static void __init fadump_setup_param_area(void)
                                                       COMMAND_LINE_SIZE,
                                                       range_start,
                                                       range_end);
-       if (!fw_dump.param_area || sysfs_create_file(fadump_kobj, 
&bootargs_append_attr.attr)) {
+       if (!fw_dump.param_area) {
                pr_warn("WARNING: Could not setup area to pass additional 
parameters!\n");
                return;
        }
  
-	memset(phys_to_virt(fw_dump.param_area), 0, COMMAND_LINE_SIZE);
+       memset((void *)fw_dump.param_area, 0, COMMAND_LINE_SIZE);
  }
  
  /*
@@ -1807,7 +1813,6 @@ int __init setup_fadump(void)
        }
        /* Initialize the kernel dump memory structure and register with f/w */
        else if (fw_dump.reserve_dump_area_size) {
-               fadump_setup_param_area();
                fw_dump.ops->fadump_init_mem_struct(&fw_dump);
                register_fadump();
        }
diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 0be07ed407c7..47db1b1aef25 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -908,6 +908,9 @@ void __init early_init_devtree(void *params)
  
  	mmu_early_init_devtree();
  
+	/* Setup param area for passing additional parameters to fadump capture kernel. */
+       fadump_setup_param_area();
+
Maybe we should add a comment here saying this needs to be done after
mmu_early_init_devtree() because for pseries LPARs we need to be able to
reliably use early_radix_enabled() helper within fadump_setup_param_area().

Sure, I will update the comment to indicate that the
fadump_setup_param_area() function must be called once the MMU is finalized.


Either ways the patch looks good to me. So please feel free to add -
Reviewed-by: Ritesh Harjani (IBM) <ritesh.l...@gmail.com>

Thanks for the review Ritesh.

- Sourabh Jain