On Tue, Sep 03, 2024 at 09:54:19AM +0200, Helge Deller wrote: > On 8/8/24 20:19, Linus Torvalds wrote: > > On Thu, 8 Aug 2024 at 10:48, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > > > > > Here is the disassembly from my latest crashing debug kernel which > > > shifts it up a couple of pages. Add 0x10 or sub 0x20 to make it work. > > > > Looks like I was off by an instruction, it's the 28th divide-step (not > > 29) that does the page crosser: > > > > > 4121dffc: 0b 21 04 41 ds r1,r25,r1 > > > 4121e000: 0b bd 07 1d add,c ret1,ret1,ret1 > > > > but my parisc knowledge is not good enough to even guess at what could go wrong. > > > > And I have no actual reason to believe this has *anything* to do with > > an itlb miss, except for that whole "exact placement seems to matter, > > and it crosses a page boundary" detail. > > Well, you were on the right track :-) > > Guenters kernel from > http://server.roeck-us.net/qemu/parisc64-6.10.3/ > boots nicely on my physical C3700 machine, but crashes with Qemu. > > So, it's not some bug in the kernel ITLB miss handler or other > Linux kernel code. > > Instead it's a Qemu bug, which gets triggered by the page > boundary crossing of: > 41218ffc: 0b 21 04 41 ds r1,r25,r1 > 41219000: 0b bd 07 1d add,c ret1,ret1,ret1 > > During the ITLB miss, the carry bits and the PSW-V-bit > (from the divide step) are saved in the IPSW register and restored > upon irq return. > > During packaging the bits there is a qemu coding bug, where we missed > to handle the PSW-V-bit as 32-bit value even on a 64-bit CPU. > The (copy&pasted) patch below fixes the crash for me. > Yes, that works for me as well. Thanks a lot for the fix! Guenter > Helge > > diff --git a/target/hppa/helper.c b/target/hppa/helper.c > index b79ddd8184..d4b1a3cd5a 100644 > --- a/target/hppa/helper.c > +++ b/target/hppa/helper.c > @@ -53,7 +53,7 @@ target_ulong cpu_hppa_get_psw(CPUHPPAState *env) > } > > psw |= env->psw_n * PSW_N; > - psw |= (env->psw_v < 0) * PSW_V; > + psw |= ((env->psw_v >> 31) & 1) * PSW_V; > psw |= env->psw | env->psw_xb; > > return psw; >
