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a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1741813846; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=aVAkE5ITz3xbVBTsELj7FWN8tR4JCna6Us6nfaQKMwE=; b=EUG4ooiJzmLFhsxqLk5IfpT3zhYGrDIYMHjKo+KQDkpKV8B+cUxFdoB3PUyE6fcaO4/cBT pgRzJtBCjIKP48JQhiACiOje8Y62bv8045BgzZ+5DVOfZbHYgp+LfNKxLzPL3vN6uP4h7g kewNofBNLwARLwbU1+Xzvbo6uouUS5k= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1741813846; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=aVAkE5ITz3xbVBTsELj7FWN8tR4JCna6Us6nfaQKMwE=; b=6F2/uq17vUtb13lJ9QPrT49se5eI7CNvCecQPaSK3ykdNkU6wdGbJFu61uxDvO84EORj0+ EENnbeQ2j2ejzzBw== Date: Wed, 12 Mar 2025 22:10:46 +0100 From: Jiri Bohac To: Baoquan He , Vivek Goyal , Dave Young , kexec@lists.infradead.org Cc: Philipp Rudo , Donald Dutile , Pingfan Liu , Tao Liu , linux-kernel@vger.kernel.org, David Hildenbrand , Michal Hocko Subject: [PATCH v3 4/5] kdump: wait for DMA to finish when using CMA Message-ID: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Spam-Level: X-Spamd-Result: default: False [-4.29 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.19)[-0.949]; MIME_GOOD(-0.10)[text/plain]; URIBL_BLOCKED(0.00)[localhost:helo,dwarf.suse.cz:mid,suse.cz:email]; MIME_TRACE(0.00)[0:+]; FUZZY_BLOCKED(0.00)[rspamd.com]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; ARC_NA(0.00)[]; FROM_HAS_DN(0.00)[]; MISSING_XM_UA(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_DN_SOME(0.00)[]; MID_RHS_MATCH_FROMTLD(0.00)[]; RCVD_COUNT_ZERO(0.00)[0]; RCPT_COUNT_SEVEN(0.00)[11]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.cz:email] X-Spam-Score: -4.29 X-Spam-Flag: NO Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" When re-using the CMA area for kdump there is a risk of pending DMA into pinned user pages in the CMA area. Pages that are pinned long-term are migrated away from CMA, so these are not a concern. 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_MSEC milliseconds 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_MSEC to 1000 (one second) - chosen arbitrarily as both a huge margin for a DMA transfer, yet not increasing the kdump time significantly. Signed-off-by: Jiri Bohac --- include/linux/crash_core.h | 5 +++++ kernel/crash_core.c | 10 ++++++++++ 2 files changed, 15 insertions(+) diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h index 44305336314e..543e4a71f13c 100644 --- a/include/linux/crash_core.h +++ b/include/linux/crash_core.h @@ -56,6 +56,11 @@ static inline unsigned int crash_get_elfcorehdr_size(voi= d) { return 0; } /* Alignment required for elf header segment */ #define ELF_CORE_HEADER_ALIGN 4096 =20 +/* Time to wait for possible DMA to finish before starting the kdump kernel + * when a CMA reservation is used + */ +#define CMA_DMA_TIMEOUT_MSEC 1000 + 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 078fe5bc5a74..ed152af08d1e 100644 --- a/kernel/crash_core.c +++ b/kernel/crash_core.c @@ -21,6 +21,7 @@ #include #include #include +#include =20 #include #include @@ -97,6 +98,14 @@ int kexec_crash_loaded(void) } EXPORT_SYMBOL_GPL(kexec_crash_loaded); =20 +static void crash_cma_clear_pending_dma(void) +{ + if (!crashk_cma_cnt) + return; + + mdelay(CMA_DMA_TIMEOUT_MSEC); +} + /* * 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 @@ -119,6 +128,7 @@ void __noclone __crash_kexec(struct pt_regs *regs) crash_setup_regs(&fixed_regs, regs); crash_save_vmcoreinfo(); machine_crash_shutdown(&fixed_regs); + crash_cma_clear_pending_dma(); machine_kexec(kexec_crash_image); } kexec_unlock(); --=20 2.46.0 --=20 Jiri Bohac SUSE Labs, Prague, Czechia