From: Borislav Petkov <bp@alien8.de>
To: Ingo Molnar <mingo@kernel.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Dave Hansen <dave@sr71.net>,
hpa@zytor.com, tglx@linutronix.de, torvalds@linux-foundation.org,
linux-kernel@vger.kernel.org, dwmw@amazon.co.uk,
linux-tip-commits@vger.kernel.org,
Arjan van de Ven <arjan@infradead.org>,
Jerry Hoemann <jerry.hoemann@hpe.com>
Subject: Re: [PATCH] watchdog: hpwdt: Remove spinlock acquire and BIOS calls from NMI context
Date: Wed, 14 Feb 2018 10:44:05 +0100 [thread overview]
Message-ID: <20180214094404.GA18349@pd.tnic> (raw)
In-Reply-To: <20180214093159.mdzfupne547bi5qx@gmail.com>
+ Jerry
On Wed, Feb 14, 2018 at 10:31:59AM +0100, Ingo Molnar wrote:
>
> * Tim Chen <tim.c.chen@linux.intel.com> wrote:
>
> > Dave Hansen and I had some discussions on how to handle the nested NMI and
> > firmware calls. We thought of using a per cpu counter to record the nesting
> > call depth and toggle IBRS appropriately for the depth 0->1 and 1->0 transition.
> > Will this change be sufficient?
>
> Yeah, so I think the first question should be: does the firmware call from NMI
> context make sense to begin with?
>
> Because in this particular case it does not appear to be so: the reason for the
> BIOS/firmware call appears to be to determine how we nmi_panic() after receiving
> an NMI that no other NMI handler handled: with a passive-aggressive "I don't know"
> panic message or with a slightly more informative panic message.
>
> That's not a real value-add to users - so we can avoid all these complications by
> applying the patch below:
>
> drivers/watchdog/hpwdt.c | 30 ++++--------------------------
> 1 file changed, 4 insertions(+), 26 deletions(-)
>
> As a bonus the spinlock use can be removed as well.
>
> Thanks,
>
> Ingo
>
> ====================>
> From b038428a739a3fcf0b9678305c131f60af7422ca Mon Sep 17 00:00:00 2001
> From: Ingo Molnar <mingo@kernel.org>
> Date: Wed, 14 Feb 2018 10:24:41 +0100
> Subject: [PATCH] watchdog: hpwdt: Remove spinlock acquire and BIOS calls from
> NMI context
>
> Taking a spinlock and calling into the firmware are problematic things to
> do from NMI callbacks.
>
> It also seems completely pointless in this particular case:
>
> - cmn_regs is updated by the firmware call in the hpwdt_pretimeout() NMI
> callback, but there's almost no use for it: we use it only to determine
> whether to panic with an 'unknown NMI' or a slightly more descriptive
> message.
>
> - cmn_regs and rom_lock is not used anywhere else, other than early detection
> of the firmware capability.
>
> So remove rom_lock, make the cmn_regs call from the detection routine only,
> and thus make the NMI callback a lot more robust.
>
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> ---
> drivers/watchdog/hpwdt.c | 30 ++++--------------------------
> 1 file changed, 4 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/watchdog/hpwdt.c b/drivers/watchdog/hpwdt.c
> index f1f00dfc0e68..2544fe482fe3 100644
> --- a/drivers/watchdog/hpwdt.c
> +++ b/drivers/watchdog/hpwdt.c
> @@ -150,9 +150,7 @@ static unsigned int hpwdt_nmi_decoding;
> static unsigned int allow_kdump = 1;
> static unsigned int is_icru;
> static unsigned int is_uefi;
> -static DEFINE_SPINLOCK(rom_lock);
> static void *cru_rom_addr;
> -static struct cmn_registers cmn_regs;
>
> extern asmlinkage void asminline_call(struct cmn_registers *pi86Regs,
> unsigned long *pRomEntry);
> @@ -225,6 +223,7 @@ static int cru_detect(unsigned long map_entry,
> unsigned long physical_bios_base = 0;
> unsigned long physical_bios_offset = 0;
> int retval = -ENODEV;
> + struct cmn_registers cmn_regs = { };
>
> bios32_map = ioremap(map_entry, (2 * PAGE_SIZE));
>
> @@ -486,32 +485,18 @@ static int hpwdt_my_nmi(void)
> */
> static int hpwdt_pretimeout(unsigned int ulReason, struct pt_regs *regs)
> {
> - unsigned long rom_pl;
> - static int die_nmi_called;
> -
> if (!hpwdt_nmi_decoding)
> return NMI_DONE;
>
> if ((ulReason == NMI_UNKNOWN) && !hpwdt_my_nmi())
> return NMI_DONE;
>
> - spin_lock_irqsave(&rom_lock, rom_pl);
> - if (!die_nmi_called && !is_icru && !is_uefi)
> - asminline_call(&cmn_regs, cru_rom_addr);
> - die_nmi_called = 1;
> - spin_unlock_irqrestore(&rom_lock, rom_pl);
> -
> if (allow_kdump)
> hpwdt_stop();
>
> - if (!is_icru && !is_uefi) {
> - if (cmn_regs.u1.ral == 0) {
> - nmi_panic(regs, "An NMI occurred, but unable to determine source.\n");
> - return NMI_HANDLED;
> - }
> - }
> - nmi_panic(regs, "An NMI occurred. Depending on your system the reason "
> - "for the NMI is logged in any one of the following "
> + nmi_panic(regs,
> + "An NMI occurred. Depending on your system the reason "
> + "for the NMI might be logged in any one of the following "
> "resources:\n"
> "1. Integrated Management Log (IML)\n"
> "2. OA Syslog\n"
> @@ -744,13 +729,6 @@ static int hpwdt_init_nmi_decoding(struct pci_dev *dev)
> HPWDT_ARCH);
> return retval;
> }
> -
> - /*
> - * We know this is the only CRU call we need to make so lets keep as
> - * few instructions as possible once the NMI comes in.
> - */
> - cmn_regs.u1.rah = 0x0D;
> - cmn_regs.u1.ral = 0x02;
> }
>
> /*
--
Regards/Gruss,
Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
next prev parent reply other threads:[~2018-02-14 9:44 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-10 23:39 [PATCH v2 0/6] Spectre v2 updates David Woodhouse
2018-02-10 23:39 ` [PATCH v2 1/6] x86/speculation: Update Speculation Control microcode blacklist David Woodhouse
2018-02-11 12:08 ` [tip:x86/pti] " tip-bot for David Woodhouse
2018-02-12 9:50 ` [PATCH v2 1/6] " Darren Kenny
2018-02-12 14:16 ` David Woodhouse
2018-02-12 14:32 ` Thomas Gleixner
2018-02-10 23:39 ` [PATCH v2 2/6] Revert "x86/speculation: Simplify indirect_branch_prediction_barrier()" David Woodhouse
2018-02-11 12:09 ` [tip:x86/pti] " tip-bot for David Woodhouse
2018-02-13 8:58 ` tip-bot for David Woodhouse
2018-02-13 9:41 ` Peter Zijlstra
2018-02-13 11:28 ` Ingo Molnar
2018-02-13 13:28 ` Peter Zijlstra
2018-02-13 13:38 ` Ingo Molnar
2018-02-13 15:26 ` [tip:x86/pti] x86/speculation: Add <asm/msr-index.h> dependency tip-bot for Peter Zijlstra
2018-02-15 0:28 ` tip-bot for Peter Zijlstra
2018-02-10 23:39 ` [PATCH v2 3/6] KVM: x86: Reduce retpoline performance impact in slot_handle_level_range() David Woodhouse
2018-02-11 12:09 ` [tip:x86/pti] KVM/x86: Reduce retpoline performance impact in slot_handle_level_range(), by always inlining iterator helper methods tip-bot for David Woodhouse
2018-02-13 8:58 ` tip-bot for David Woodhouse
2018-02-10 23:39 ` [PATCH v2 4/6] X86/nVMX: Properly set spec_ctrl and pred_cmd before merging MSRs David Woodhouse
2018-02-11 12:10 ` [tip:x86/pti] " tip-bot for KarimAllah Ahmed
2018-02-13 8:59 ` tip-bot for KarimAllah Ahmed
2018-02-10 23:39 ` [PATCH v2 5/6] KVM/nVMX: Set the CPU_BASED_USE_MSR_BITMAPS if we have a valid L02 MSR bitmap David Woodhouse
2018-02-11 10:19 ` Ingo Molnar
[not found] ` <1518345844.3677.365.camel@amazon.co.uk>
2018-02-11 10:55 ` Ingo Molnar
2018-02-11 12:10 ` [tip:x86/pti] " tip-bot for KarimAllah Ahmed
2018-02-13 8:59 ` tip-bot for KarimAllah Ahmed
2018-02-10 23:39 ` [PATCH v2 6/6] x86/speculation: Use IBRS if available before calling into firmware David Woodhouse
2018-02-11 11:46 ` Ingo Molnar
2018-02-11 10:41 ` [PATCH v2 0/6] Spectre v2 updates Ingo Molnar
2018-02-11 15:19 ` [PATCH v2.1] x86/speculation: Use IBRS if available before calling into firmware David Woodhouse
2018-02-11 18:50 ` [PATCH] x86/speculation: Clean up various Spectre related details Ingo Molnar
2018-02-11 19:25 ` David Woodhouse
2018-02-11 19:43 ` Ingo Molnar
2018-02-12 15:30 ` David Woodhouse
2018-02-13 8:04 ` Ingo Molnar
2018-02-11 19:19 ` [tip:x86/pti] x86/speculation: Use IBRS if available before calling into firmware tip-bot for David Woodhouse
2018-02-12 5:59 ` afzal mohammed
2018-02-12 16:30 ` David Woodhouse
2018-02-12 10:22 ` Ingo Molnar
2018-02-12 11:50 ` Peter Zijlstra
2018-02-12 12:27 ` David Woodhouse
2018-02-12 13:06 ` Peter Zijlstra
2018-02-13 7:58 ` Ingo Molnar
2018-02-12 12:28 ` Peter Zijlstra
2018-02-12 16:13 ` Dave Hansen
2018-02-12 16:58 ` Peter Zijlstra
2018-02-13 7:55 ` Ingo Molnar
2018-02-14 1:49 ` Tim Chen
2018-02-14 8:56 ` Peter Zijlstra
2018-02-14 8:57 ` Peter Zijlstra
2018-02-14 19:20 ` Tim Chen
2018-02-14 23:19 ` Ingo Molnar
2018-02-15 2:01 ` Tim Chen
2018-02-14 9:31 ` [PATCH] watchdog: hpwdt: Remove spinlock acquire and BIOS calls from NMI context Ingo Molnar
2018-02-14 9:38 ` Peter Zijlstra
2018-02-14 10:39 ` Ingo Molnar
2018-02-14 9:44 ` Borislav Petkov [this message]
2018-02-14 18:13 ` Jerry Hoemann
2018-02-14 23:17 ` Ingo Molnar
2018-02-15 17:44 ` Jerry Hoemann
2018-02-15 19:02 ` Ingo Molnar
2018-02-15 19:48 ` Peter Zijlstra
2018-02-16 18:44 ` [tip:x86/pti] x86/speculation: Use IBRS if available before calling into firmware Tim Chen
2018-02-16 19:16 ` David Woodhouse
2018-02-16 23:46 ` Tim Chen
2018-02-17 10:26 ` Ingo Molnar
2018-02-19 9:20 ` Peter Zijlstra
2018-02-19 9:29 ` David Woodhouse
2018-02-19 9:39 ` Ingo Molnar
2018-02-19 9:44 ` David Woodhouse
2018-02-19 10:08 ` Peter Zijlstra
2018-02-19 9:36 ` Ingo Molnar
2018-02-12 8:27 ` [PATCH v2 0/6] Spectre v2 updates Paolo Bonzini
2018-02-13 7:59 ` Ingo Molnar
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180214094404.GA18349@pd.tnic \
--to=bp@alien8.de \
--cc=arjan@infradead.org \
--cc=dave@sr71.net \
--cc=dwmw@amazon.co.uk \
--cc=hpa@zytor.com \
--cc=jerry.hoemann@hpe.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-tip-commits@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
--cc=tim.c.chen@linux.intel.com \
--cc=torvalds@linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).