From: Peter Zijlstra <peterz@infradead.org>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: tglx@linutronix.de, luto@amacapital.net,
linux-kernel@vger.kernel.org, x86@kernel.org,
Lai Jiangshan <laijs@linux.alibaba.com>,
sean.j.christopherson@intel.com, daniel.thompson@linaro.org
Subject: Re: [PATCH 1/6] x86/entry: Introduce local_db_{save,restore}()
Date: Thu, 28 May 2020 23:15:50 +0200 [thread overview]
Message-ID: <20200528211550.GR2483@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <17e097f5-f92c-bd7e-fb1d-ee08c4169dbe@citrix.com>
On Thu, May 28, 2020 at 09:52:30PM +0100, Andrew Cooper wrote:
> On 28/05/2020 21:19, Peter Zijlstra wrote:
> > --- a/arch/x86/include/asm/debugreg.h
> > +++ b/arch/x86/include/asm/debugreg.h
> > @@ -113,6 +113,31 @@ static inline void debug_stack_usage_inc
> > static inline void debug_stack_usage_dec(void) { }
> > #endif /* X86_64 */
> >
> > +static __always_inline void local_db_save(unsigned long *dr7)
> > +{
> > + get_debugreg(*dr7, 7);
> > + if (*dr7)
> > + set_debugreg(0, 7);
>
> %dr7 has an architecturally stuck bit in it.
>
> You want *dr7 != 0x400 to avoid writing 0 unconditionally.
Do we have to have that bit set when writing it? Otherwise I might
actually prefer masking it out.
> Also, API wise, wouldn't it be nicer to write "dr7 = local_db_save()"
> rather than having a void function returning a single long via pointer?
Probably.. I started with local_irq_save() and .. well, n/m. I'll change
it ;-)
next prev parent reply other threads:[~2020-05-28 21:18 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-28 20:19 [PATCH 0/6] x86/entry: disallow #DB more Peter Zijlstra
2020-05-28 20:19 ` [PATCH 1/6] x86/entry: Introduce local_db_{save,restore}() Peter Zijlstra
2020-05-28 20:52 ` Andrew Cooper
2020-05-28 21:15 ` Peter Zijlstra [this message]
2020-05-28 21:33 ` Peter Zijlstra
2020-05-29 17:28 ` Andy Lutomirski
2020-05-29 19:02 ` Peter Zijlstra
2020-05-28 21:36 ` Andrew Cooper
2020-05-28 20:19 ` [PATCH 2/6] x86/entry, nmi: Disable #DB Peter Zijlstra
2020-05-28 20:19 ` [PATCH 3/6] x86/entry, mce: Disallow #DB during #MC Peter Zijlstra
2020-05-28 20:19 ` [PATCH 4/6] x86/entry: Optimize local_db_save() for virt Peter Zijlstra
2020-05-29 17:24 ` Sean Christopherson
2020-05-28 20:19 ` [PATCH 5/6] x86/entry: Remove debug IDT frobbing Peter Zijlstra
2020-05-28 20:19 ` [RFC][PATCH 6/6] x86/entry: Remove DBn stacks Peter Zijlstra
2020-05-28 22:35 ` Lai Jiangshan
2020-05-28 22:37 ` Peter Zijlstra
2020-05-28 22:42 ` [PATCH 0/6] x86/entry: disallow #DB more Lai Jiangshan
2020-05-28 22:48 ` Peter Zijlstra
2020-05-28 23:05 ` Lai Jiangshan
2020-05-29 8:00 ` Peter Zijlstra
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=20200528211550.GR2483@worktop.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=andrew.cooper3@citrix.com \
--cc=daniel.thompson@linaro.org \
--cc=laijs@linux.alibaba.com \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@amacapital.net \
--cc=sean.j.christopherson@intel.com \
--cc=tglx@linutronix.de \
--cc=x86@kernel.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).