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Re: [PATCH] target/s390x: fix s390_probe_access to check PAGE_WRITE_ORG


From: Peter Maydell
Subject: Re: [PATCH] target/s390x: fix s390_probe_access to check PAGE_WRITE_ORG for writeability
Date: Fri, 23 Apr 2021 14:06:24 +0100

On Fri, 23 Apr 2021 at 13:22, Cornelia Huck <cohuck@redhat.com> wrote:
>
> On Thu, 22 Apr 2021 16:44:27 +0100
> Alex Bennée <alex.bennee@linaro.org> wrote:
>
> > We can remove PAGE_WRITE when (internally) marking a page read-only
> > because it contains translated code. This can get confused when we are
> > executing signal return code on signal stacks.
> >
> > Fixes: e56552cf07 ("target/s390x: Implement the MVPG condition-code-option 
> > bit")
> > Found-by: Richard Henderson <richard.henderson@linaro.org>
> > Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> > Cc: Cornelia Huck <cohuck@redhat.com>
> > Cc: Thomas Huth <thuth@redhat.com>
> > Cc: David Hildenbrand <david@redhat.com>
> > Cc: Laurent Vivier <laurent@vivier.eu>
> > ---
> >  target/s390x/mem_helper.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/target/s390x/mem_helper.c b/target/s390x/mem_helper.c
> > index 12e84a4285..f6a7d29273 100644
> > --- a/target/s390x/mem_helper.c
> > +++ b/target/s390x/mem_helper.c
> > @@ -145,7 +145,7 @@ static int s390_probe_access(CPUArchState *env, 
> > target_ulong addr, int size,
> >
> >  #if defined(CONFIG_USER_ONLY)
> >      flags = page_get_flags(addr);
> > -    if (!(flags & (access_type == MMU_DATA_LOAD ?  PAGE_READ : 
> > PAGE_WRITE))) {
> > +    if (!(flags & (access_type == MMU_DATA_LOAD ?  PAGE_READ : 
> > PAGE_WRITE_ORG))) {
> >          env->__excp_addr = addr;
> >          flags = (flags & PAGE_VALID) ? PGM_PROTECTION : PGM_ADDRESSING;
> >          if (nonfault) {
>
> What's the verdict on this one? I plan to queue this to s390-next; but
> if we end up doing an -rc5, it might qualify as a regression fix.

What's your opinion? I think we do need an rc5 for the network backend
hotplug crash. I don't want to open the doors for lots of new fixes
just because we've got another rc, but on the other hand this one
does look like it's a pretty small and safe fix, and letting intermittent
crash bugs out into the wild seems like it could lead to a lot of
annoying re-investigation of the same bug if it's reported by users
later... So I kind of lean towards putting it in rc5.

thanks
-- PMM



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