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t=1740070552; 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=Zg9TqkBWUtlYqKI0kTqM9WGsbClJXO8S/5dxvIXqVjg=; b=8GLOAiAwgV61PAlnDUgNuZ79byMhByQu4gP4ibAQQGNRevOWgppNYgBu893Erf64B16Ktn 1ouARot+VJXZ8hCw== Date: Thu, 20 Feb 2025 17:55:52 +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 v2 4/5] kdump: wait for DMA to finish when using CMA Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Spamd-Result: default: False [-4.26 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.16)[-0.782]; MIME_GOOD(-0.10)[text/plain]; ARC_NA(0.00)[]; MISSING_XM_UA(0.00)[]; FROM_HAS_DN(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_COUNT_ZERO(0.00)[0]; RCPT_COUNT_SEVEN(0.00)[11]; MID_RHS_MATCH_FROMTLD(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; DBL_BLOCKED_OPENRESOLVER(0.00)[localhost:helo,suse.cz:email,dwarf.suse.cz:mid] X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250220_085554_142181_9BB8D3B6 X-CRM114-Status: GOOD ( 16.15 ) X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org 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(void) { return 0; } /* Alignment required for elf header segment */ #define ELF_CORE_HEADER_ALIGN 4096 +/* 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..543e509b7926 100644 --- a/kernel/crash_core.c +++ b/kernel/crash_core.c @@ -21,6 +21,7 @@ #include #include #include +#include #include #include @@ -97,6 +98,14 @@ int kexec_crash_loaded(void) } EXPORT_SYMBOL_GPL(kexec_crash_loaded); +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 @@ -116,6 +125,7 @@ void __noclone __crash_kexec(struct pt_regs *regs) if (kexec_crash_image) { struct pt_regs fixed_regs; + crash_cma_clear_pending_dma(); crash_setup_regs(&fixed_regs, regs); crash_save_vmcoreinfo(); machine_crash_shutdown(&fixed_regs); -- Jiri Bohac SUSE Labs, Prague, Czechia