On Friday, May 31, 2019 7:14:56 AM CEST Josh Poimboeuf wrote:
> On Fri, May 31, 2019 at 01:42:02AM +0200, Jiri Kosina wrote:
> > On Thu, 30 May 2019, Josh Poimboeuf wrote:
> >
> > > > > Reviewed-by: Thomas Gleixner <t...@linutronix.de>
> > > >
> > > > Yes, it is, thanks!
> > >
> > > I still think changing monitor/mwait to use a fixmap address would be a
> > > much cleaner way to fix this. I can try to work up a patch tomorrow.
> >
> > I disagree with that from the backwards compatibility point of view.
> >
> > I personally am quite frequently using differnet combinations of
> > resumer/resumee kernels, and I've never been biten by it so far. I'd guess
> > I am not the only one.
> > Fixmap sort of breaks that invariant.
>
> Right now there is no backwards compatibility because nosmt resume is
> already broken.
>
> For "future" backwards compatibility we could just define a hard-coded
> reserved fixmap page address, adjacent to the vsyscall reserved address.
>
> Something like this (not yet tested)? Maybe we could also remove the
> resume_play_dead() hack?
Yes, we can IMO, but in a separate patch, please.
> diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h
> index 9da8cccdf3fb..1c328624162c 100644
> --- a/arch/x86/include/asm/fixmap.h
> +++ b/arch/x86/include/asm/fixmap.h
> @@ -80,6 +80,7 @@ enum fixed_addresses {
> #ifdef CONFIG_X86_VSYSCALL_EMULATION
> VSYSCALL_PAGE = (FIXADDR_TOP - VSYSCALL_ADDR) >> PAGE_SHIFT,
> #endif
> + FIX_MWAIT = (FIXADDR_TOP - VSYSCALL_ADDR - 1) >> PAGE_SHIFT,
> #endif
> FIX_DBGP_BASE,
> FIX_EARLYCON_MEM_BASE,
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 73e69aaaa117..9804fbe25d03 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -108,6 +108,8 @@ int __read_mostly __max_smt_threads = 1;
> /* Flag to indicate if a complete sched domain rebuild is required */
> bool x86_topology_update;
>
> +static char __mwait_page[PAGE_SIZE];
> +
> int arch_update_cpu_topology(void)
> {
> int retval = x86_topology_update;
> @@ -1319,6 +1321,8 @@ void __init native_smp_prepare_cpus(unsigned int
> max_cpus)
> smp_quirk_init_udelay();
>
> speculative_store_bypass_ht_init();
> +
> + set_fixmap(FIX_MWAIT, __pa_symbol(&__mwait_page));
> }
>
> void arch_enable_nonboot_cpus_begin(void)
> @@ -1631,11 +1635,12 @@ static inline void mwait_play_dead(void)
> }
>
> /*
> - * This should be a memory location in a cache line which is
> - * unlikely to be touched by other processors. The actual
> - * content is immaterial as it is not actually modified in any way.
> + * This memory location is never actually written to. It's mapped at a
> + * reserved fixmap address to ensure the monitored address remains
> + * valid across a hibernation resume operation. Otherwise a triple
> + * fault can occur.
> */
> - mwait_ptr = ¤t_thread_info()->flags;
> + mwait_ptr = (void *)fix_to_virt(FIX_MWAIT);
>
> wbinvd();
>
>
Jiri, any chance to test this?
