Messages in this thread | | | Subject | Re: [PATCH v2] powerpc/32s: Fix DSI and ISI exceptions for CONFIG_VMAP_STACK | From | Christophe Leroy <> | Date | Fri, 14 Feb 2020 07:27:16 +0100 |
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Le 13/02/2020 à 11:04, Christophe Leroy a écrit : > hash_page() needs to read page tables from kernel memory. When entire > kernel memory is mapped by BATs, which is normally the case when > CONFIG_STRICT_KERNEL_RWX is not set, it works even if the page hosting > the page table is not referenced in the MMU hash table. > > However, if the page where the page table resides is not covered by > a BAT, a DSI fault can be encountered from hash_page(), and it loops > forever. This can happen when CONFIG_STRICT_KERNEL_RWX is selected > and the alignment of the different regions is too small to allow > covering the entire memory with BATs. This also happens when > CONFIG_DEBUG_PAGEALLOC is selected or when booting with 'nobats' > flag. > > Also, if the page containing the kernel stack is not present in the > MMU hash table, registers cannot be saved and a recursive DSI fault > is encountered. > > To allow hash_page() to properly do its job at all time and load the > MMU hash table whenever needed, it must run with data MMU disabled. > This means it must be called before re-enabling data MMU. To allow > this, registers clobbered by hash_page() and create_hpte() have to > be saved in the thread struct together with SRR0, SSR1, DAR and DSISR. > It is also necessary to ensure that DSI prolog doesn't overwrite > regs saved by prolog of the current running exception. That means: > - DSI can only use SPRN_SPRG_SCRATCH0 > - Exceptions must free SPRN_SPRG_SCRATCH0 before writing to the stack. > > This also fixes the Oops reported by Erhard when create_hpte() is > called by add_hash_page(). > > Fixes: cd08f109e262 ("powerpc/32s: Enable CONFIG_VMAP_STACK") > Reported-by: Erhard F. <erhard_f@mailbox.org> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=206501 > Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Tested-by: Erhard F. <erhard_f@mailbox.org>
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