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Message-ID: <YzRxPAoN+XmOfJzV@zn.tnic>
Date: Wed, 28 Sep 2022 18:07:24 +0200
From: Borislav Petkov <bp@...en8.de>
To: Eric DeVolder <eric.devolder@...cle.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
kexec@...ts.infradead.org, ebiederm@...ssion.com,
dyoung@...hat.com, bhe@...hat.com, vgoyal@...hat.com,
tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
hpa@...or.com, nramas@...ux.microsoft.com, thomas.lendacky@....com,
robh@...nel.org, efault@....de, rppt@...nel.org, david@...hat.com,
sourabhjain@...ux.ibm.com, konrad.wilk@...cle.com,
boris.ostrovsky@...cle.com
Subject: Re: [PATCH v12 7/7] x86/crash: Add x86 crash hotplug support
On Tue, Sep 13, 2022 at 02:12:31PM -0500, Eric DeVolder wrote:
> This topic was discussed previously https://lkml.org/lkml/2022/3/3/372.
Please do not use lkml.org to refer to lkml messages. We have a
perfectly fine archival system at lore.kernel.org. You simply do
https://lore.kernel.org/r/<Message-ID>
when you want to point to a previous mail.
> David points out that terminology is tricky here due to differing behaviors.
> And perhaps that is your point in asking for guidance text. It can be
> complicated
Which means you need an explanation how to use this even more.
And why is CONFIG_CRASH_MAX_MEMORY_RANGES even a Kconfig item and not
something you discover from the hardware?
Your help text talks about System RAM entries in /proc/iomem which means
that those entries are present somewhere in the kernel and you can read
them out and do the proper calculations dynamically instead of doing the
static CONFIG_NR_CPUS_DEFAULT + CONFIG_CRASH_MAX_MEMORY_RANGES thing.
> , but it all comes down to System RAM entries.
>
> I could perhaps offer an overly simplified example such that for 1GiB block
> size, for example, the CRASH_MAX_MEMORY_RANGES of 32768 would allow for 32TiB
> of memory?
Yes, and stick it somewhere in Documentation/admin-guide/kdump/ and
refer to it in that help text so that people can find it and read how to
use your new option.
> The kbuf.bufsz value is obtained via a call to prepare_elf_headers(); I can
> not initialize it at its declaration.
Sorry, I meant this:
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 8fc7d678ac72..ee6fd9f1b2b9 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -395,8 +395,9 @@ int crash_load_segments(struct kimage *image)
if (ret)
return ret;
- image->elf_headers = kbuf.buffer;
- image->elf_headers_sz = kbuf.bufsz;
+ image->elf_headers = kbuf.buffer;
+ image->elf_headers_sz = kbuf.bufsz;
+ kbuf.memsz = kbuf.bufsz;
#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
/* Ensure elfcorehdr segment large enough for hotplug changes */
@@ -407,9 +408,8 @@ int crash_load_segments(struct kimage *image)
image->elf_headers_sz = kbuf.memsz;
image->elfcorehdr_index = image->nr_segments;
image->elfcorehdr_index_valid = true;
-#else
- kbuf.memsz = kbuf.bufsz;
#endif
+
kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
ret = kexec_add_buffer(&kbuf);
> I'm at a loss as to what to do differently here. You've raised this issue
> before and I went back and looked at the suggestions then and I don't see
> how that applies to this situation. How is this situation different than the
> #ifdef CONFIG_KEXEC_FILE that immediately preceeds it?
See the diff at the end. I'm not saying this is how you should do it
but it should give you a better idea. The logic being, the functions
in the .c file don't really need ifdeffery around them - you're adding
1-2 functions and crash.c is not that big - so they can be built in
unconditionally. You'd need the ifdeffery *in the header only* when
crash.c is not being built.
But I've done it with ifdeffery in the .c file now because yes, the
kexec code is a minefield of ifdeffery. Hell, there's ifdeffery even in
the headers for structs. Ifdeffery you don't really need. Someone should
clean that up and simplify this immensely.
> Currently there is a concurrent effort for PPC support by Sourabh
> Jain, and in that effort arch_map_crash_pages() is using __va(paddr).
Why?
> I do not know the nuances between kmap_local_page() and __va() to
> answer the question.
kmap_local_page() is a generic interface and it should work on any arch.
And it is documented even:
$ git grep kmap_local_page Documentation/
> If kmap_local_page() works for all archs, then I'm happy to drop these
> arch_ variants and use it directly.
Yes, pls do.
---
diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
index 432073385b2d..b73c9628cd85 100644
--- a/arch/x86/include/asm/kexec.h
+++ b/arch/x86/include/asm/kexec.h
@@ -205,6 +205,17 @@ void *arch_kexec_kernel_image_load(struct kimage *image);
int arch_kimage_file_post_load_cleanup(struct kimage *image);
#define arch_kimage_file_post_load_cleanup arch_kimage_file_post_load_cleanup
+
+#ifdef CONFIG_CRASH_MAX_MEMORY_RANGES
+void *arch_map_crash_pages(unsigned long paddr, unsigned long size);
+void arch_unmap_crash_pages(void **ptr);
+void arch_crash_handle_hotplug_event(struct kimage *image, unsigned int hp_action);
+#else
+void *arch_map_crash_pages(unsigned long paddr, unsigned long size) { return NULL; }
+void arch_unmap_crash_pages(void **ptr) { }
+void arch_crash_handle_hotplug_event(struct kimage *image, unsigned int hp_action) { }
+#endif
+
#endif
#endif
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 8fc7d678ac72..a526c893abe8 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -395,8 +395,9 @@ int crash_load_segments(struct kimage *image)
if (ret)
return ret;
- image->elf_headers = kbuf.buffer;
- image->elf_headers_sz = kbuf.bufsz;
+ image->elf_headers = kbuf.buffer;
+ image->elf_headers_sz = kbuf.bufsz;
+ kbuf.memsz = kbuf.bufsz;
#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
/* Ensure elfcorehdr segment large enough for hotplug changes */
@@ -407,9 +408,8 @@ int crash_load_segments(struct kimage *image)
image->elf_headers_sz = kbuf.memsz;
image->elfcorehdr_index = image->nr_segments;
image->elfcorehdr_index_valid = true;
-#else
- kbuf.memsz = kbuf.bufsz;
#endif
+
kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
ret = kexec_add_buffer(&kbuf);
@@ -425,7 +425,8 @@ int crash_load_segments(struct kimage *image)
}
#endif /* CONFIG_KEXEC_FILE */
-#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+#ifdef CONFIG_CRASH_MAX_MEMORY_RANGES
+
/*
* NOTE: The addresses and sizes passed to this routine have
* already been fully aligned on page boundaries. There is no
@@ -462,8 +463,7 @@ void arch_unmap_crash_pages(void **ptr)
* is prepared in a kernel buffer, and then it is written on top
* of the existing/old elfcorehdr.
*/
-void arch_crash_handle_hotplug_event(struct kimage *image,
- unsigned int hp_action)
+void arch_crash_handle_hotplug_event(struct kimage *image, unsigned int hp_action)
{
struct kexec_segment *ksegment;
unsigned char *ptr = NULL;
@@ -513,4 +513,5 @@ void arch_crash_handle_hotplug_event(struct kimage *image,
if (elfbuf)
vfree(elfbuf);
}
-#endif
+
+#endif /* CONFIG_CRASH_MAX_MEMORY_RANGES */
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index a48577a36fb8..0f79ad4c4f80 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -27,6 +27,19 @@ extern struct resource crashk_res;
extern struct resource crashk_low_res;
extern note_buf_t __percpu *crash_notes;
+/* Alignment required for elf header segment */
+#define ELF_CORE_HEADER_ALIGN 4096
+
+struct crash_mem_range {
+ u64 start, end;
+};
+
+struct crash_mem {
+ unsigned int max_nr_ranges;
+ unsigned int nr_ranges;
+ struct crash_mem_range ranges[];
+};
+
#ifdef CONFIG_KEXEC_CORE
#include <linux/list.h>
#include <linux/compat.h>
@@ -237,19 +250,6 @@ static inline int arch_kexec_locate_mem_hole(struct kexec_buf *kbuf)
}
#endif
-/* Alignment required for elf header segment */
-#define ELF_CORE_HEADER_ALIGN 4096
-
-struct crash_mem_range {
- u64 start, end;
-};
-
-struct crash_mem {
- unsigned int max_nr_ranges;
- unsigned int nr_ranges;
- struct crash_mem_range ranges[];
-};
-
extern int crash_exclude_mem_range(struct crash_mem *mem,
unsigned long long mstart,
unsigned long long mend);
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 5bc5159d9cb1..f6b5d835f826 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -622,6 +622,15 @@ static int __init crash_save_vmcoreinfo_init(void)
subsys_initcall(crash_save_vmcoreinfo_init);
#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+
+void __weak *arch_map_crash_pages(unsigned long paddr, unsigned long size)
+{
+ return NULL;
+}
+
+void __weak arch_unmap_crash_pages(void **ptr) { }
+void __weak arch_crash_handle_hotplug_event(struct kimage *image, unsigned int hp_action) { }
+
/*
* To accurately reflect hot un/plug changes, the elfcorehdr (which
* is passed to the crash kernel via the elfcorehdr= parameter)
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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