From: Thomas Gleixner <tglx@linutronix.de>
To: "Singh\, Balbir" <sblbir@amazon.com>,
"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc: "keescook\@chromium.org" <keescook@chromium.org>,
"tony.luck\@intel.com" <tony.luck@intel.com>,
"benh\@kernel.crashing.org" <benh@kernel.crashing.org>,
"jpoimboe\@redhat.com" <jpoimboe@redhat.com>,
"x86\@kernel.org" <x86@kernel.org>,
"dave.hansen\@intel.com" <dave.hansen@intel.com>
Subject: Re: [PATCH v3 3/5] arch/x86/mm: Refactor cond_ibpb() to support other use cases
Date: Tue, 21 Apr 2020 11:02:54 +0200 [thread overview]
Message-ID: <87wo69us75.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <9cbabf58e0a6fe3775c268d1fa4517d02ad7e617.camel@amazon.com>
"Singh, Balbir" <sblbir@amazon.com> writes:
> On Sat, 2020-04-18 at 11:59 +0200, Thomas Gleixner wrote:
>>
>> "Singh, Balbir" <sblbir@amazon.com> writes:
>> > On Fri, 2020-04-17 at 15:07 +0200, Thomas Gleixner wrote:
>> > >
>> > > Balbir Singh <sblbir@amazon.com> writes:
>> > > >
>> > > > /*
>> > > > - * Use bit 0 to mangle the TIF_SPEC_IB state into the mm pointer
>> > > > which is
>> > > > - * stored in cpu_tlb_state.last_user_mm_ibpb.
>> > > > + * Bits to mangle the TIF_SPEC_IB state into the mm pointer which is
>> > > > + * stored in cpu_tlb_state.last_user_mm_spec.
>> > > > */
>> > > > #define LAST_USER_MM_IBPB 0x1UL
>> > > > +#define LAST_USER_MM_SPEC_MASK (LAST_USER_MM_IBPB)
>> > > >
>> > > > /* Reinitialize tlbstate. */
>> > > > - this_cpu_write(cpu_tlbstate.last_user_mm_ibpb,
>> > > > LAST_USER_MM_IBPB);
>> > > > + this_cpu_write(cpu_tlbstate.last_user_mm_spec,
>> > > > LAST_USER_MM_IBPB);
>> > >
>> > > Shouldn't that be LAST_USER_MM_MASK?
>> > >
>> >
>> > No, that crashes the system for SW flushes, because it tries to flush the
>> > L1D
>> > via the software loop and early enough we don't have the l1d_flush_pages
>> > allocated. LAST_USER_MM_MASK has LAST_USER_MM_FLUSH_L1D bit set.
>>
>> You can trivially prevent this by checking l1d_flush_pages != NULL.
>>
>
> But why would we want to flush on reinit? It is either coming back from a low
> power state or initialising, is it worth adding a check for != NULL everytime
> we flush to handle this case?
Fair enough. Please add a comment so the same question does not come
back 3 month from now.
Thanks,
tglx
next prev parent reply other threads:[~2020-04-21 9:03 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-08 9:02 [PATCH v3 0/5] Optionally flush L1D on context switch Balbir Singh
2020-04-08 9:02 ` [PATCH v3 1/5] arch/x86/kvm: Refactor l1d flush lifecycle management Balbir Singh
2020-04-17 12:57 ` Thomas Gleixner
2020-04-17 22:34 ` Singh, Balbir
2020-04-08 9:02 ` [PATCH v3 2/5] arch/x86: Refactor tlbflush and l1d flush Balbir Singh
2020-04-17 13:03 ` Thomas Gleixner
2020-04-17 22:58 ` Singh, Balbir
2020-04-08 9:02 ` [PATCH v3 3/5] arch/x86/mm: Refactor cond_ibpb() to support other use cases Balbir Singh
2020-04-17 13:07 ` Thomas Gleixner
2020-04-17 23:02 ` Singh, Balbir
2020-04-18 9:59 ` Thomas Gleixner
2020-04-21 3:46 ` Singh, Balbir
2020-04-21 9:02 ` Thomas Gleixner [this message]
2020-04-08 9:02 ` [PATCH v3 4/5] arch/x86: Optionally flush L1D on context switch Balbir Singh
2020-04-17 14:41 ` Thomas Gleixner
2020-04-18 1:30 ` Singh, Balbir
2020-04-18 10:17 ` Thomas Gleixner
2020-04-20 0:24 ` Singh, Balbir
2020-04-08 9:02 ` [PATCH v3 5/5] arch/x86: Add L1D flushing Documentation Balbir Singh
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=87wo69us75.fsf@nanos.tec.linutronix.de \
--to=tglx@linutronix.de \
--cc=benh@kernel.crashing.org \
--cc=dave.hansen@intel.com \
--cc=jpoimboe@redhat.com \
--cc=keescook@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=sblbir@amazon.com \
--cc=tony.luck@intel.com \
--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).