On Tue, Aug 12, 2025 at 6:57 PM Andrey Konovalov <andreyk...@gmail.com> wrote: > > On Tue, Aug 12, 2025 at 2:49 PM Baoquan He <b...@redhat.com> wrote: > > > > Currently only hw_tags mode of kasan can be enabled or disabled with > > kernel parameter kasan=on|off for built kernel. For kasan generic and > > sw_tags mode, there's no way to disable them once kernel is built. > > This is not convenient sometime, e.g in system kdump is configured. > > When the 1st kernel has KASAN enabled and crash triggered to switch to > > kdump kernel, the generic or sw_tags mode will cost much extra memory > > for kasan shadow while in fact it's meaningless to have kasan in kdump > > kernel. > > > > So this patchset moves the kasan=on|off out of hw_tags scope and into > > common code to make it visible in generic and sw_tags mode too. Then we > > can add kasan=off in kdump kernel to reduce the unneeded meomry cost for > > kasan. > > Hi Baoquan, > > Could you clarify what are you trying to achieve by disabling > Generic/SW_TAGS KASAN via command-line? Do you want not to see any > KASAN reports produced? Or gain back the performance? > > Because for the no reports goal, it would be much easier to add a > command-line parameter to silent the reports. > > And the performance goal can only be partially achieved, as you cannot > remove the compiler instrumentation without rebuilding the kernel. > (What are the boot times for KASAN_GENERIC=n vs KASAN_GENERIC=y + > kasan=off vs KASAN_GENERIC=y btw?) > > Thank you!
Ah, you don't want the shadow memory for kdump, sorry, I somehow missed that. I'm not familiar with the internals of kdump, but would it be possible/reasonable to teach kdump to ignore the KASAN shadow region?
