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kdump: wait for DMA to finish when using CMA

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When re-using the CMA area for kdump there is a risk of pending DMA into
pinned user pages in the CMA area.

Pages residing in CMA areas can usually not get long-term pinned and are
instead migrated away from the CMA area, so long-term pinning is typically
not a concern.  (BUGs in the kernel might still lead to long-term pinning
of such pages if everything goes wrong.)

Pages pinned without FOLL_LONGTERM remain in the CMA and may possibly be
the source or destination of a pending DMA transfer.

Although there is no clear specification how long a page may be pinned
without FOLL_LONGTERM, pinning without the flag shows an intent of the
caller to only use the memory for short-lived DMA transfers, not a
transfer initiated by a device asynchronously at a random time in the
future.

Add a delay of CMA_DMA_TIMEOUT_SEC seconds before starting the kdump
kernel, giving such short-lived DMA transfers time to finish before the
CMA memory is re-used by the kdump kernel.

Set CMA_DMA_TIMEOUT_SEC to 10 seconds - chosen arbitrarily as both a huge
margin for a DMA transfer, yet not increasing the kdump time too
significantly.

Link: https://lkml.kernel.org/r/aEqpgDIBndZ5LXSo@dwarf.suse.cz
Signed-off-by: Jiri Bohac <jbohac@suse.cz>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Donald Dutile <ddutile@redhat.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Philipp Rudo <prudo@redhat.com>
Cc: Pingfan Liu <piliu@redhat.com>
Cc: Tao Liu <ltao@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Jiri Bohac 2025-06-12 12:18:40 +02:00 • committed by Andrew Morton
parent ce1bf19a34
commit e1280f3071
1 changed files with 15 additions and 0 deletions
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15
kernel/crash_core.c
View file

@ -21,6 +21,7 @@
#include <linux/reboot.h> #include <linux/reboot.h>
#include <linux/btf.h> #include <linux/btf.h>
#include <linux/objtool.h> #include <linux/objtool.h>
#include <linux/delay.h>
#include <asm/page.h> #include <asm/page.h>
#include <asm/sections.h> #include <asm/sections.h>
@ -33,6 +34,11 @@
/* Per cpu memory for storing cpu states in case of system crash. */ /* Per cpu memory for storing cpu states in case of system crash. */
note_buf_t __percpu *crash_notes; note_buf_t __percpu *crash_notes;
/* time to wait for possible DMA to finish before starting the kdump kernel
* when a CMA reservation is used
*/
#define CMA_DMA_TIMEOUT_SEC 10
#ifdef CONFIG_CRASH_DUMP #ifdef CONFIG_CRASH_DUMP
int kimage_crash_copy_vmcoreinfo(struct kimage *image) int kimage_crash_copy_vmcoreinfo(struct kimage *image)
@ -97,6 +103,14 @@ int kexec_crash_loaded(void)
} }
EXPORT_SYMBOL_GPL(kexec_crash_loaded); EXPORT_SYMBOL_GPL(kexec_crash_loaded);
static void crash_cma_clear_pending_dma(void)
{
if (!crashk_cma_cnt)
return;
mdelay(CMA_DMA_TIMEOUT_SEC * 1000);
}
/* /*
* No panic_cpu check version of crash_kexec(). This function is called * No panic_cpu check version of crash_kexec(). This function is called
* only when panic_cpu holds the current CPU number; this is the only CPU * only when panic_cpu holds the current CPU number; this is the only CPU
@ -119,6 +133,7 @@ void __noclone __crash_kexec(struct pt_regs *regs)
crash_setup_regs(&fixed_regs, regs); crash_setup_regs(&fixed_regs, regs);
crash_save_vmcoreinfo(); crash_save_vmcoreinfo();
machine_crash_shutdown(&fixed_regs); machine_crash_shutdown(&fixed_regs);
crash_cma_clear_pending_dma();
machine_kexec(kexec_crash_image); machine_kexec(kexec_crash_image);
} }
kexec_unlock(); kexec_unlock();