LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Thomas Gleixner <tglx@linutronix.de>
To: "Prakhya, Sai Praneeth" <sai.praneeth.prakhya@intel.com>
Cc: "linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"x86@kernel.org" <x86@kernel.org>, Borislav Petkov <bp@alien8.de>,
	Ingo Molnar <mingo@kernel.org>, Andy Lutomirski <luto@kernel.org>,
	"Hansen, Dave" <dave.hansen@intel.com>,
	Bhupesh Sharma <bhsharma@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>
Subject: RE: [PATCH V2 1/2] x86/efi: Unmap EFI boot services code/data regions from efi_pgd
Date: Mon, 29 Oct 2018 19:11:09 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.21.1810291907320.5984@nanos.tec.linutronix.de> (raw)
In-Reply-To: <FFF73D592F13FD46B8700F0A279B802F485E5549@ORSMSX114.amr.corp.intel.com>

Sai,

On Mon, 29 Oct 2018, Prakhya, Sai Praneeth wrote:

> Hi Thomas and Peter,
> 
> [off the mailing list because I wasn't sure if it's a good idea to spam others with my questions]

In general it's good to do on list because others can learn from the
answers as well.

> > > > +	retval = __change_page_attr_set_clr(&cpa, 0);
> > > > +	__flush_tlb_all();
> > >
> > > So this looks like you copied it from kernel_map_pages_in_pgd() which
> > > has been discussed before to be not sufficient, but it can't be
> > > changed right now due to locking issues.
> >
> > Managed to confuse myself. The place which cannot be changed is a different
> > one, but still for your call site __flush_tlb_all() might not be sufficient.
> 
> Since the mappings are changed, I thought a flush_tlb() might be needed.
> But, (to be honest), I don't completely understand the x86/mm code. So, could you 
> please elaborate the issue more for my better understanding?
> 
> So some questions I have are,
> 1. What did Peter Z mean here? "How is that not a TLB invalidation bug ?"

__flush_tlb_all() flushes only the mapping on the current CPU. So in a SMP
environment it's not sufficient.

> 2. I assumed kernel_map_pages_in_pgd() to be a good code but you said that 
> it has some locking issues. So, could you please elaborate more on that.

I corrected myself. It's the other function which cannot use the proper
cpa_flush.*() functions.

> Or, could you please provide me some pointers in the source code that I
> can take a look at so that I could understand the issue much better.

I'll have a second look at the whole thing and reply on list.

Thanks,

	tglx

  reply	other threads:[~2018-10-29 18:11 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-26 21:38 [PATCH V2 0/2] Unmap EFI boot services code/data regions after boot Sai Praneeth Prakhya
2018-10-26 21:38 ` [PATCH V2 1/2] x86/efi: Unmap EFI boot services code/data regions from efi_pgd Sai Praneeth Prakhya
2018-10-29  6:07   ` Ingo Molnar
2018-10-29  7:26     ` Prakhya, Sai Praneeth
2018-10-29 14:40   ` Peter Zijlstra
2018-10-29 17:13   ` Thomas Gleixner
2018-10-29 17:21     ` Thomas Gleixner
2018-10-29 18:01       ` Prakhya, Sai Praneeth
2018-10-29 18:11         ` Thomas Gleixner [this message]
2018-10-29 18:18           ` Thomas Gleixner
2018-10-29 18:32             ` Prakhya, Sai Praneeth
2018-10-29 18:38     ` Prakhya, Sai Praneeth
2018-10-26 21:38 ` [PATCH V2 2/2] x86/efi: Move efi_<reserve/free>_boot_services() to arch/x86 Sai Praneeth Prakhya
2018-10-29 17:14   ` Thomas Gleixner

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=alpine.DEB.2.21.1810291907320.5984@nanos.tec.linutronix.de \
    --to=tglx@linutronix.de \
    --cc=ard.biesheuvel@linaro.org \
    --cc=bhsharma@redhat.com \
    --cc=bp@alien8.de \
    --cc=dave.hansen@intel.com \
    --cc=linux-efi@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=luto@kernel.org \
    --cc=mingo@kernel.org \
    --cc=peterz@infradead.org \
    --cc=sai.praneeth.prakhya@intel.com \
    --cc=x86@kernel.org \
    --subject='RE: [PATCH V2 1/2] x86/efi: Unmap EFI boot services code/data regions from efi_pgd' \
    /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

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).