Date: Tue, 16 Jan 2018 20:55:43 +0100
From: Joerg Roedel <joro@8bytes.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        "H . Peter Anvin" <hpa@zytor.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>, Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Juergen Gross <jgross@suse.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bp@alien8.de>, Jiri Kosina <jkosina@suse.cz>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Brian Gerst <brgerst@gmail.com>,
        David Laight <David.Laight@aculab.com>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        Eduardo Valentin <eduval@amazon.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        Will Deacon <will.deacon@arm.com>,
        "Liguori, Anthony" <aliguori@amazon.com>,
        Daniel Gruss <daniel.gruss@iaik.tugraz.at>,
        Hugh Dickins <hughd@google.com>,
        Kees Cook <keescook@google.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Waiman Long <llong@redhat.com>, Joerg Roedel <jroedel@suse.de>
Subject: Re: [RFC PATCH 00/16] PTI support for x86-32
Message-ID: <20180116195543.GG28161@8bytes.org>
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Hi Linus,

On Tue, Jan 16, 2018 at 10:59:01AM -0800, Linus Torvalds wrote:
> Yes, I'm very happy to see that this is actually not nearly as bad as
> I feared it might be,

Yeah, I was looking at the original PTI patches and my impression was
that a lot of the complicated stuff (like setting up the cpu_entry_area)
was already in there for 32 bit too. So it was mostly about the entry
code and some changes to the 32bit page-table code.

> Some of those #ifdef's in the PTI code you added might want more
> commentary about what the exact differences are. And maybe they could
> be done more cleanly with some abstraction. But nothing looked
> _horrible_.

I'll add more comments and better abstraction, Dave has already
suggested some improvements here. Reading some of my comments again,
they need a rework anyway.

> .. and please run all the segment and syscall selfchecks that Andy has written.

Didn't know about them yet, thanks. I will run them too in my testing

> Xen PV and PTI don't work together even on x86-64 afaik, the Xen
> people apparently felt it wasn't worth it.  See the
> 
>         if (hypervisor_is_type(X86_HYPER_XEN_PV)) {
>                 pti_print_if_insecure("disabled on XEN PV.");
>                 return;
>         }
> 
> in pti_check_boottime_disable().

But I might have broken something for them anyway, honestly I didn't pay
much attention to the XEN_PV case as I was trying to get it running
here. My hope is that someone who knows Xen better than I do will help
out :)


Regards,

	Joerg