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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> 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: <4b07a3eb-aad6-4436-9591-289c6504bb92@redhat.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 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 arch/s390/Kconfig: config NEED_PROC_VMCORE_DEVICE_RAM def y ================================== > > So the three changes you did are > > (a) Remove the config option but select/depend on them. > > (b) Remove the "depends on PROC_VMCORE" from PROC_VMCORE_DEVICE_RAM, > and the "if PROC_VMCORE" from s390. > > (c) Remove the PROVIDE_PROC_VMCORE_DEVICE_RAM > > > Regarding (a), that doesn't work. If you select a config option that doesn't > exist, it is silently dropped. It's always treated as if it wouldn't be set. > > Regarding (b), I think that's an anti-pattern (having config options enabled > that are completely ineffective) and I don't see a benefit dropping them. > > Regarding (c), it would mean that s390x unconditionally includes that code > even if virtio-mem is not configured in. > > So while we could drop PROVIDE_PROC_VMCORE_DEVICE_RAM -- (c), it would that > we end up including code in configurations that don't possibly need it. > That's why I included that part. > > > > > > > ======= config items extracted from this patchset==== > > 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 > > > > config VIRTIO_MEM > > depends on X86_64 || ARM64 || RISCV > > ~~~~~ I don't get why VIRTIO_MEM dones't depend on S390 if > > s390 need PROC_VMCORE_DEVICE_RAM. > > This series depends on s390 support for virtio-mem, which just went > upstream. Got It, I just applied this series on top of the latest mainline's master branch. Thanks for telling. > > > commit 38968bcdcc1d46f2fdcd3a72599d5193bf8baf84 > Author: David Hildenbrand > Date: Fri Oct 25 16:14:49 2024 +0200 > > virtio-mem: s390 support > > > > ...... > > select PROVIDE_PROC_VMCORE_DEVICE_RAM if PROC_VMCORE > > > > config S390 > > select NEED_PROC_VMCORE_DEVICE_RAM if PROC_VMCORE > > ================================================= > > > > Thanks for having a look! > > -- > Cheers, > > David / dhildenb >