linux-kernel - Re: [PATCH] wait_on_bit: add an acquire memory barrier

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Date:   Sat, 27 Aug 2022 04:42:37 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@...hat.com>
To:     Ard Biesheuvel <ardb@...nel.org>
cc:     Will Deacon <will@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Andrea Parri <parri.andrea@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Akira Yokosawa <akiyks@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH] wait_on_bit: add an acquire memory barrier



On Sat, 27 Aug 2022, Ard Biesheuvel wrote:

> On Sat, 27 Aug 2022 at 08:32, Ard Biesheuvel <ardb@...nel.org> wrote:
> >
> > On Fri, 26 Aug 2022 at 21:10, Mikulas Patocka <mpatocka@...hat.com> wrote:
> > >
> > >
> > >
> > > On Fri, 26 Aug 2022, Ard Biesheuvel wrote:
> > >
> > > > Could you try booting with earlycon?
> > > >
> > > > Just 'earlycon' and if that does not help,
> > >
> > > It doesn't help.
> > >
> > > > 'earlycon=uart8250,mmio32,<uart PA>' [IIRC, mcbin uses 16550
> > > > compatible UARTs, right?]
> > >
> > > mcbin is the host system (running a stable kernel fine). The crash happens
> > > in a virtual machine. The vm uses /dev/ttyAMA0 as a console:
> > >
> > > Serial: AMBA PL011 UART driver
> > > 9000000.pl011: ttyAMA0 at MMIO 0x9000000 (irq = 45, base_baud = 0) is a PL011 rev1
> > > printk: console [ttyAMA0] enabled
> > >
> > > I tried earlycon=pl011,mmio32,0x9000000 - but it doesn't help, it hangs
> > > without printing anything.
> > >
> >
> > If you are using pl011, you should drop the mmio32 - it only takes a
> > physical address (and optionally baud rate etc, but QEMU doesn't need
> > those)
> 
> Could you try the diff below please?
> 
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -371,7 +371,9 @@ SYM_FUNC_END(create_idmap)
>  SYM_FUNC_START_LOCAL(create_kernel_mapping)
>         adrp    x0, init_pg_dir
>         mov_q   x5, KIMAGE_VADDR                // compile time __va(_text)
> +#ifdef CONFIG_RELOCATABLE
>         add     x5, x5, x23                     // add KASLR displacement
> +#endif
>         adrp    x6, _end                        // runtime __pa(_end)
>         adrp    x3, _text                       // runtime __pa(_text)
>         sub     x6, x6, x3                      // _end - _text
> 

Yes - this patch fixes the crash.

Mikulas