From: "Singh, Balbir" <sblbir@amazon.com>
To: "tglx@linutronix.de" <tglx@linutronix.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc: "keescook@chromium.org" <keescook@chromium.org>,
"thomas.lendacky@amd.com" <thomas.lendacky@amd.com>,
"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 v6 5/6] Optionally flush L1D on context switch
Date: Thu, 14 May 2020 08:23:11 +0000 [thread overview]
Message-ID: <e6acf54b5abe8ded46ee5fee37fb1f40f505f96b.camel@amazon.com> (raw)
In-Reply-To: <87d0773mg8.fsf@nanos.tec.linutronix.de>
On Wed, 2020-05-13 at 17:04 +0200, Thomas Gleixner wrote:
>
>
> Balbir Singh <sblbir@amazon.com> writes:
> >
> > + if (prev_mm & LAST_USER_MM_L1D_FLUSH)
> > + arch_l1d_flush(0); /* Just flush, don't populate the
> > TLB */
>
> Bah. I fundamentally hate tail comments. They are just disturbing the
> reading flow. Aside of that, this states the WHAT but not the WHY. And
> if you add that explanation then you need more than 20 characters and
> end up with
>
> if (prev_mm & LAST_USER_MM_L1D_FLUSH) {
> /*
> * Proper comment explaining why this is flushing
> * without prepopulating the TLB.
> */
> arch_l1d_flush(0);
> }
>
I added a comment due to the use of 0, 0 is usually seen as true or
false and I wanted to add some comments in there to indicate we don't
populate the TLB, the reason we don't do it is, I don't think we need
to. I am happy to revisit the placement of the comment.
> anyway. And even for a short comment which fits after the function
> call
> it's way better to have:
>
> if (prev_mm & LAST_USER_MM_L1D_FLUSH) {
> /* Short explanation */
> arch_l1d_flush(0);
> }
>
> Hmm?
>
> > + /*
> > + * Leave last_user_mm_spec at LAST_USER_MM_IBPB, we don't
> > + * want to set LAST_USER_MM_L1D_FLUSH and force a flush before
> > + * we've allocated the flush pages.
>
> Ah here is the comment. I still like the explicit define for the (re)
> init.
>
I saw your tree and it sounds like you fixed it up in there in patch 3.
Balbir Singh.
next prev parent reply other threads:[~2020-05-14 8:23 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-10 1:47 [PATCH v6 0/6] Optionally flush L1D on context switch Balbir Singh
2020-05-10 1:47 ` [PATCH v6 1/6] arch/x86/kvm: Refactor l1d flush lifecycle management Balbir Singh
2020-05-13 13:35 ` Thomas Gleixner
2020-05-14 8:23 ` Singh, Balbir
2020-05-13 13:53 ` Thomas Gleixner
2020-05-14 8:25 ` Singh, Balbir
2020-05-22 9:32 ` [tip: x86/mm] x86/kvm: Refactor L1D flush page management tip-bot2 for Balbir Singh
2020-05-10 1:47 ` [PATCH v6 2/6] arch/x86/kvm: Refactor tlbflush and l1d flush Balbir Singh
2020-05-22 9:32 ` [tip: x86/mm] x86/kvm: Refactor L1D flush operations tip-bot2 for Balbir Singh
2020-05-10 1:48 ` [PATCH v6 3/6] arch/x86/mm: Refactor cond_ibpb() to support other use cases Balbir Singh
2020-05-13 14:16 ` Thomas Gleixner
2020-05-22 9:32 ` [tip: x86/mm] x86/mm: " tip-bot2 for Balbir Singh
2020-09-16 13:11 ` [tip: x86/pti] " tip-bot2 for Balbir Singh
2020-05-10 1:48 ` [PATCH v6 4/6] arch/x86/kvm: Refactor L1D flushing Balbir Singh
2020-05-22 9:32 ` [tip: x86/mm] x86/kvm: " tip-bot2 for Balbir Singh
2020-05-10 1:48 ` [PATCH v6 5/6] Optionally flush L1D on context switch Balbir Singh
2020-05-13 15:04 ` Thomas Gleixner
2020-05-14 8:23 ` Singh, Balbir [this message]
2020-05-13 15:27 ` Thomas Gleixner
2020-05-14 21:28 ` Singh, Balbir
2020-05-13 16:16 ` Thomas Gleixner
2020-05-14 7:43 ` Singh, Balbir
2020-05-14 11:33 ` Thomas Gleixner
2020-05-10 1:48 ` [PATCH v6 6/6] Documentation: Add L1D flushing Documentation Balbir Singh
2020-05-13 13:33 ` Thomas Gleixner
2020-05-14 1:12 ` Singh, Balbir
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