linux-kernel - [PATCH] x86/umip: Downgrade warning messages to debug loglevel

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Message-ID: <YUIHPOmSQyZSkMaC@zn.tnic>
Date:   Wed, 15 Sep 2021 16:46:20 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        Marcus Rückert <mrueckert@...e.com>
Subject: [PATCH] x86/umip: Downgrade warning messages to debug loglevel

On Wed, Sep 15, 2021 at 04:34:10AM -0700, Ricardo Neri wrote:
> The goal at the time was encourage users to report bugs on the
> applications and eventually have them fixed. It also meant to warn users
> about degraded performance due to emulation. To my knowledge, no one has
> reported the latter thus far.

Probably because people do not even get to need UMIP a whole lot,
apparently.

> Since after almost 4 years, performance degradation does not seem to be a
> concern, I think it is sensible to remove the warnings.

Yap.

> They could also be salvaged by converting them to umiip_pr_debug(), just
> to err on the cautious side without having to add a new command line
> argument.

Yap, that's a good idea too:

---
From: Borislav Petkov <bp@...e.de>
Date: Wed, 15 Sep 2021 16:39:18 +0200
Subject: [PATCH] x86/umip: Downgrade warning messages to debug loglevel
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

After four years in the wild, those have not fullfilled their
initial purpose of pushing people to fix their software to not use
UMIP-emulated instructions, and to warn users about the degraded
emulation performance.

Yet, the only thing that "degrades" performance is overflowing dmesg
with those:

  [Di Sep  7 00:24:05 2021] umip_printk: 1345 callbacks suppressed
  [Di Sep  7 00:24:05 2021] umip: someapp.exe[29231] ip:14064cdba sp:11b7c0: SIDT instruction cannot be used by applications.
  [Di Sep  7 00:24:05 2021] umip: someapp.exe[29231] ip:14064cdba sp:11b7c0: For now, expensive software emulation returns the result.
  ...
  [Di Sep  7 00:26:06 2021] umip_printk: 2227 callbacks suppressed
  [Di Sep  7 00:26:06 2021] umip: someapp.exe[29231] ip:14064cdba sp:11b940: SIDT instruction cannot be used by applications.

and users don't really care about that - they just want to play their
games in wine.

So convert those to debug loglevel - in case someone is still interested
in them, someone can boot with "debug" on the kernel cmdline.

Reported-by: Marcus Rückert <mrueckert@...e.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Link: https://lkml.kernel.org/r/20210907200454.30458-1-bp@alien8.de
---
 arch/x86/kernel/umip.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
index 576b47e7523d..5a4b21389b1d 100644
--- a/arch/x86/kernel/umip.c
+++ b/arch/x86/kernel/umip.c
@@ -92,8 +92,8 @@ static const char * const umip_insns[5] = {
 
 #define umip_pr_err(regs, fmt, ...) \
 	umip_printk(regs, KERN_ERR, fmt, ##__VA_ARGS__)
-#define umip_pr_warn(regs, fmt, ...) \
-	umip_printk(regs, KERN_WARNING, fmt,  ##__VA_ARGS__)
+#define umip_pr_debug(regs, fmt, ...) \
+	umip_printk(regs, KERN_DEBUG, fmt,  ##__VA_ARGS__)
 
 /**
  * umip_printk() - Print a rate-limited message
@@ -361,10 +361,10 @@ bool fixup_umip_exception(struct pt_regs *regs)
 	if (umip_inst < 0)
 		return false;
 
-	umip_pr_warn(regs, "%s instruction cannot be used by applications.\n",
+	umip_pr_debug(regs, "%s instruction cannot be used by applications.\n",
 			umip_insns[umip_inst]);
 
-	umip_pr_warn(regs, "For now, expensive software emulation returns the result.\n");
+	umip_pr_debug(regs, "For now, expensive software emulation returns the result.\n");
 
 	if (emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size,
 			      user_64bit_mode(regs)))
-- 
2.29.2


-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette