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Tsirkin" , Jason Wang , Xuan Zhuo , Eugenio =?iso-8859-1?Q?P=E9rez?= , Vivek Goyal , Dave Young , Thomas Huth , Cornelia Huck , Janosch Frank , Claudio Imbrenda , Eric Farman , Andrew Morton Subject: Re: [PATCH v1 07/11] fs/proc/vmcore: introduce PROC_VMCORE_DEVICE_RAM to detect device RAM ranges in 2nd kernel Message-ID: References: <20241025151134.1275575-1-david@redhat.com> <20241025151134.1275575-8-david@redhat.com> <4b07a3eb-aad6-4436-9591-289c6504bb92@redhat.com> <3ed18ba1-e4b1-461e-a3a7-5de2df59ca60@redhat.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3ed18ba1-e4b1-461e-a3a7-5de2df59ca60@redhat.com> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 On 11/20/24 at 03:39pm, David Hildenbrand wrote: > On 20.11.24 15:05, Baoquan He wrote: > > On 11/20/24 at 11:48am, David Hildenbrand wrote: > > > On 20.11.24 11:13, Baoquan He wrote: > > > > On 10/25/24 at 05:11pm, David Hildenbrand wrote: > > > > > s390 allocates+prepares the elfcore hdr in the dump (2nd) kernel, not in > > > > > the crashed kernel. > > > > > > > > > > RAM provided by memory devices such as virtio-mem can only be detected > > > > > using the device driver; when vmcore_init() is called, these device > > > > > drivers are usually not loaded yet, or the devices did not get probed > > > > > yet. Consequently, on s390 these RAM ranges will not be included in > > > > > the crash dump, which makes the dump partially corrupt and is > > > > > unfortunate. > > > > > > > > > > Instead of deferring the vmcore_init() call, to an (unclear?) later point, > > > > > let's reuse the vmcore_cb infrastructure to obtain device RAM ranges as > > > > > the device drivers probe the device and get access to this information. > > > > > > > > > > Then, we'll add these ranges to the vmcore, adding more PT_LOAD > > > > > entries and updating the offsets+vmcore size. > > > > > > > > > > Use Kconfig tricks to include this code automatically only if (a) there is > > > > > a device driver compiled that implements the callback > > > > > (PROVIDE_PROC_VMCORE_DEVICE_RAM) and; (b) the architecture actually needs > > > > > this information (NEED_PROC_VMCORE_DEVICE_RAM). > > > > > > > > > > The current target use case is s390, which only creates an elf64 > > > > > elfcore, so focusing on elf64 is sufficient. > > > > > > > > > > Signed-off-by: David Hildenbrand > > > > > --- > > > > > fs/proc/Kconfig | 25 ++++++ > > > > > fs/proc/vmcore.c | 156 +++++++++++++++++++++++++++++++++++++ > > > > > include/linux/crash_dump.h | 9 +++ > > > > > 3 files changed, 190 insertions(+) > > > > > > > > > > diff --git a/fs/proc/Kconfig b/fs/proc/Kconfig > > > > > index d80a1431ef7b..1e11de5f9380 100644 > > > > > --- a/fs/proc/Kconfig > > > > > +++ b/fs/proc/Kconfig > > > > > @@ -61,6 +61,31 @@ config PROC_VMCORE_DEVICE_DUMP > > > > > as ELF notes to /proc/vmcore. You can still disable device > > > > > dump using the kernel command line option 'novmcoredd'. > > > > > +config PROVIDE_PROC_VMCORE_DEVICE_RAM > > > > > + def_bool n > > > > > + > > > > > +config NEED_PROC_VMCORE_DEVICE_RAM > > > > > + def_bool n > > > > > + > > > > > +config PROC_VMCORE_DEVICE_RAM > > > > > + def_bool y > > > > > + depends on PROC_VMCORE > > > > > + depends on NEED_PROC_VMCORE_DEVICE_RAM > > > > > + depends on PROVIDE_PROC_VMCORE_DEVICE_RAM > > > > > > > > Kconfig item is always a thing I need learn to master. > > > > > > Yes, it's usually a struggle to get it right. It took me a couple of > > > iterations to get to this point :) > > > > > > > When I checked > > > > this part, I have to write them down to deliberate. I am wondering if > > > > below 'simple version' works too and more understandable. Please help > > > > point out what I have missed. > > > > > > > > ===========simple version====== > > > > config PROC_VMCORE_DEVICE_RAM > > > > def_bool y > > > > depends on PROC_VMCORE && VIRTIO_MEM > > > > depends on NEED_PROC_VMCORE_DEVICE_RAM > > > > > > > > config S390 > > > > select NEED_PROC_VMCORE_DEVICE_RAM > > > > ============ > > > > Sorry, things written down didn't correctly reflect them in my mind. > > > > ===========simple version====== > > fs/proc/Kconfig: > > config PROC_VMCORE_DEVICE_RAM > > def_bool y > > depends on PROC_VMCORE && VIRTIO_MEM > > depends on NEED_PROC_VMCORE_DEVICE_RAM > > config NEED_PROC_VMCORE_DEVICE_RAM > > def y > > > > arch/s390/Kconfig: > > config NEED_PROC_VMCORE_DEVICE_RAM > > def y > > ================================== > > That would work, but I don't completely like it. > > (a) I want s390x to select NEED_PROC_VMCORE_DEVICE_RAM instead. Staring at a > bunch of similar cases (git grep "config NEED" | grep Kconfig, git grep > "config ARCH_WANTS" | grep Kconfig), "select" is the common way to do it. > > So unless there is a pretty good reason, I'll keep > NEED_PROC_VMCORE_DEVICE_RAM as is. That's easy to satify, see below: ============simple version===== fs/proc/Kconfig: config NEED_PROC_VMCORE_DEVICE_RAM def n config PROC_VMCORE_DEVICE_RAM def_bool y depends on PROC_VMCORE && VIRTIO_MEM depends on NEED_PROC_VMCORE_DEVICE_RAM arch/s390/Kconfig: config S390 select NEED_PROC_VMCORE_DEVICE_RAM ============================== > > (b) In the context of this patch, "depends on VIRTIO_MEM" does not make > sense. We could have an intermediate: > > config PROC_VMCORE_DEVICE_RAM > def_bool n > depends on PROC_VMCORE > depends on NEED_PROC_VMCORE_DEVICE_RAM > > And change that with VIRTIO_MEM support in the relevant patch. Oh, it's not comment for this patch, I made the simple version based on the whole patchset. When I had a glance at this patch, I also took several iterations to get it after I applied the whole patchset and tried to understand the whole code. > > > I faintly remember that we try avoiding such dependencies and prefer > selecting Kconfigs instead. Just look at the SPLIT_PTE_PTLOCKS mess we still > have to clean up. But as we don't expect that many providers for now, I > don't care. With the simple version, Kconfig learner as me can easily understand what they are doing. If it took you a couple of iterations to make them as you had mentioned earlier, and it took me several iterations to understand them, I believe there must be room to improve the presented ones in this patchset. These are only my humble opinion, and I am not aware of virtio-mem at all, I'll leave this to you and other virtio-mem dev to decide what should be taken. Thanks for your patience and provided information, I learned a lot from this discussion. =================== fs/proc/Kconfig: config PROVIDE_PROC_VMCORE_DEVICE_RAM def_bool n config NEED_PROC_VMCORE_DEVICE_RAM def_bool n config PROC_VMCORE_DEVICE_RAM def_bool y depends on PROC_VMCORE depends on NEED_PROC_VMCORE_DEVICE_RAM depends on PROVIDE_PROC_VMCORE_DEVICE_RAM drivers/virtio/Kconfig: config VIRTIO_MEM select PROVIDE_PROC_VMCORE_DEVICE_RAM if PROC_VMCORE ~~~~~~~~~~~~~~ arch/s390/Kconfig: config S390 select NEED_PROC_VMCORE_DEVICE_RAM if PROC_VMCORE ~~~~~~~~~~~~~~ ======================== One last thing I haven't got well, If PROC_VMCORE_DEVICE_RAM has had dependency on PROC_VMCORE, can we take off the ' if PROC_VMCORE' when select PROVIDE_PROC_VMCORE_DEVICE_RAM and NEED_PROC_VMCORE_DEVICE_RAM? Thanks Baoquan