+ CC Christoph Hellwig Hi,
Le 22/08/2024 à 00:39, Christian Lamparter a écrit : > [Vous ne recevez pas souvent de courriers de > christian.lampar...@isd.uni-stuttgart.de. Découvrez pourquoi ceci est > important à https://aka.ms/LearnAboutSenderIdentification ] > > Sorry to write a reply to this old mail. But after years, I finally > decided to tackle an "old" problem that has come up... > And unfortunately it is related to this patch. But let me explain. > > On 9/16/21 4:52 PM, Christophe Leroy wrote: >> dcbz instruction shouldn't be used on non-cached memory. Using >> it on non-cached memory can result in alignment exception and >> implies a heavy handling. >> >> Instead of silentely emulating the instruction and resulting in high >> performance degradation, warn whenever an alignment exception is >> taken in kernel mode due to dcbz, so that the user is made aware that >> dcbz instruction has been used unexpectedly by the kernel. > > > > The devices that are affected are APM821xx: MyBook Live, Meraki MX60, > Netgear WNDR4700, ... > All these have this "splat" during boot: > ... > > what happens is that the EMAC (ethernet driver) uses a > dma_alloc_coherent here: ... > and this results in a call to dma_direct_allocation(), which has one > innocent looking memset(): memset() can't be used on non-cached memory, memset_io() has to be used instead. ... > And of course, this triggers the WARNING above. As for why memset uses > that dcbz... this is explained in: ... > > could this WARN_ON_ONCE maybe be downgraded to a single pr_info_once? > I don't see how to tackle this "neatly" in a better way. Can you try with the change below ? diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c index 4480a3cd92e0..e2bee5fcc172 100644 --- a/kernel/dma/direct.c +++ b/kernel/dma/direct.c @@ -283,13 +283,15 @@ void *dma_direct_alloc(struct device *dev, size_t size, __builtin_return_address(0)); if (!ret) goto out_free_pages; + + memset_io(ret, 0, size); } else { ret = page_address(page); if (dma_set_decrypted(dev, ret, size)) goto out_leak_pages; - } - memset(ret, 0, size); + memset(ret, 0, size); + } if (set_uncached) { arch_dma_prep_coherent(page, size); > > BugLink: > <https://github.com/openwrt/openwrt/pull/14037#issuecomment-2302485414> >
