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Message-ID: <20230731213631.pywytiwdqgtgx4ps@treble>
Date:   Mon, 31 Jul 2023 16:36:31 -0500
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Valentin Schneider <vschneid@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, kvm@...r.kernel.org, linux-mm@...ck.org,
        bpf@...r.kernel.org, x86@...nel.org, rcu@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Josh Triplett <josh@...htriplett.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Zqiang <qiang.zhang1211@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Jason Baron <jbaron@...mai.com>,
        Kees Cook <keescook@...omium.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Juerg Haefliger <juerg.haefliger@...onical.com>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Nadav Amit <namit@...are.com>,
        Dan Carpenter <error27@...il.com>,
        Chuang Wang <nashuiliang@...il.com>,
        Yang Jihong <yangjihong1@...wei.com>,
        Petr Mladek <pmladek@...e.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>, Song Liu <song@...nel.org>,
        Julian Pidancet <julian.pidancet@...cle.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Dionna Glaze <dionnaglaze@...gle.com>,
        Thomas Weißschuh <linux@...ssschuh.net>,
        Juri Lelli <juri.lelli@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Yair Podemsky <ypodemsk@...hat.com>
Subject: Re: [RFC PATCH v2 11/20] objtool: Flesh out warning related to
 pv_ops[] calls

On Mon, Jul 31, 2023 at 12:16:59PM +0100, Valentin Schneider wrote:
> You're quite right - fabricating an artificial warning with a call to __flush_tlb_local():
> 
>   vmlinux.o: warning: objtool: pv_ops[1]: indirect call to native_flush_tlb_local() leaves .noinstr.text section
>   vmlinux.o: warning: objtool: __flush_tlb_all_noinstr+0x4: call to {dynamic}() leaves .noinstr.text section
> 
> Interestingly the second one doesn't seem to have triggered the "pv_ops"
> bit of call_dest_name. Seems like any call to insn_reloc(NULL, x) will
> return NULL.

Yeah, that's weird.

> Trickling down the file yields:
> 
>   vmlinux.o: warning: objtool: pv_ops[1]: indirect call to native_flush_tlb_local() leaves .noinstr.text section
>   vmlinux.o: warning: objtool: __flush_tlb_all_noinstr+0x4: call to pv_ops[0]() leaves .noinstr.text section
> 
> In my case (!PARAVIRT_XXL) pv_ops should look like:
>   [0]: .cpu.io_delay
>   [1]: .mmu.flush_tlb_user()
> 
> so pv_ops[1] looks right. Seems like pv_call_dest() gets it right because
> it uses arch_dest_reloc_offset().
> 
> If I use the above to fix up validate_call(), would we still need
> pv_call_dest() & co?

The functionality in pv_call_dest() is still needed because it goes
through all the possible targets for the .mmu.flush_tlb_user() pointer
-- xen_flush_tlb() and native_flush_tlb_local() -- and makes sure
they're noinstr.

Ideally it would only print a single warning for this case, something
like:

  vmlinux.o: warning: objtool: __flush_tlb_all_noinstr+0x4: indirect call to native_flush_tlb_local() leaves .noinstr.text section

I left out "pv_ops[1]" because it's already long enough :-)

It would need a little bit of code shuffling.  But it's really a
preexisting problem so don't feel compelled to fix it with this patch
set.

-- 
Josh

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