From: peterz@infradead.org
To: Michael Kelley <mikelley@microsoft.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
"mbenes@suse.de" <mbenes@suse.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
"jgross@suse.com" <jgross@suse.com>
Subject: Re: [RFC][PATCH] objtool,x86_64,paravirt: Add pv_ops[] support
Date: Mon, 3 Aug 2020 18:19:21 +0200 [thread overview]
Message-ID: <20200803161921.GG2674@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <MW2PR2101MB10521C4F5E19F12E174623F7D74D0@MW2PR2101MB1052.namprd21.prod.outlook.com>
On Mon, Aug 03, 2020 at 03:18:57PM +0000, Michael Kelley wrote:
> From: peterz@infradead.org Sent: Monday, August 3, 2020 7:33 AM
> > It requires call sites are the normal indirect call, and not mangled
> > retpoison (slow_down_io() had those), it also requires pv_ops[]
> > assignments are single instructions and not laundered through some
> > pointless intermediate helper (hyperv).
^^^
> > diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
> > index 09aa44cb8a91..bed769a84637 100644
> > --- a/drivers/clocksource/hyperv_timer.c
> > +++ b/drivers/clocksource/hyperv_timer.c
> > @@ -418,6 +418,13 @@ static struct clocksource hyperv_cs_msr = {
> > .flags = CLOCK_SOURCE_IS_CONTINUOUS,
> > };
> >
> > +static __always_inline void hv_setup_sched_clock(void *sched_clock)
> > +{
> > +#ifdef CONFIG_PARAVIRT
> > + pv_ops.time.sched_clock = sched_clock;
> > +#endif
> > +}
> > +
>
> Moving this function to hyperv_timer.c is problematic because we
> want hyperv_timer.c to be architecture independent. We're in the
> process of supporting Linux guests running on Hyper-V on ARM64, and
> there's a different implementation of hv_setup_sched_clock() on ARM64.
Then stick it in a header or something. The important part is that the
compiler generates:
4b737: 48 c7 05 00 00 00 00 movq $0x0,0x0(%rip) # 4b742 <hv_init_clocksource+0x4d>
4b73e: 00 00 00 00
4b73a: R_X86_64_PC32 pv_ops
4b73e: R_X86_64_32S .text+0x827880
Where:
96378: 0000000000827880 32 FUNC LOCAL DEFAULT 4 read_hv_sched_clock_msr
Otherwise objtool cannot find the assignment and you get to keep the
pieces.
prev parent reply other threads:[~2020-08-03 16:19 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-03 14:32 [RFC][PATCH] objtool,x86_64,paravirt: Add pv_ops[] support peterz
2020-08-03 15:15 ` Andy Lutomirski
2020-08-03 15:59 ` peterz
2020-08-03 15:18 ` Michael Kelley
2020-08-03 16:19 ` peterz [this message]
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