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From: Andy Lutomirski <luto@kernel.org>
To: Mike Rapoport <rppt@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Andy Lutomirski <luto@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Borislav Petkov <bp@alien8.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Christopher Lameter <cl@linux.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	David Hildenbrand <david@redhat.com>,
	Elena Reshetova <elena.reshetova@intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Idan Yaniv <idan.yaniv@ibm.com>,
	Ingo Molnar <mingo@redhat.com>,
	James Bottomley <jejb@linux.ibm.com>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Matthew Wilcox <willy@infradead.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Michael Kerrisk <mtk.manpages@gmail.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Tycho Andersen <tycho@tycho.ws>, Will Deacon <will@kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	Linux FS Devel <linux-fsdevel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-nvdimm <linux-nvdimm@lists.01.org>,
	linux-riscv@lists.infradead.org, X86 ML <x86@kernel.org>
Subject: Re: [PATCH v5 0/5] mm: introduce memfd_secret system call to create "secret" memory areas
Date: Wed, 16 Sep 2020 11:49:25 -0700	[thread overview]
Message-ID: <CALCETrV6nFQ4tzhxKPSnK+Ec=U8ojY0k_-G2EqEG-WMGT4TkUw@mail.gmail.com> (raw)
In-Reply-To: <20200916072842.3502-1-rppt@kernel.org>

On Wed, Sep 16, 2020 at 12:28 AM Mike Rapoport <rppt@kernel.org> wrote:
>
> From: Mike Rapoport <rppt@linux.ibm.com>
>
> Hi,
>
> This is an implementation of "secret" mappings backed by a file descriptor.
> I've dropped the boot time reservation patch for now as it is not strictly
> required for the basic usage and can be easily added later either with or
> without CMA.
>
> v5 changes:
> * rebase on v5.9-rc5
> * drop boot time memory reservation patch
>
> v4 changes:
> * rebase on v5.9-rc1
> * Do not redefine PMD_PAGE_ORDER in fs/dax.c, thanks Kirill
> * Make secret mappings exclusive by default and only require flags to
>   memfd_secret() system call for uncached mappings, thanks again Kirill :)
>
> v3 changes:
> * Squash kernel-parameters.txt update into the commit that added the
>   command line option.
> * Make uncached mode explicitly selectable by architectures. For now enable
>   it only on x86.
>
> v2 changes:
> * Follow Michael's suggestion and name the new system call 'memfd_secret'
> * Add kernel-parameters documentation about the boot option
> * Fix i386-tinyconfig regression reported by the kbuild bot.
>   CONFIG_SECRETMEM now depends on !EMBEDDED to disable it on small systems
>   from one side and still make it available unconditionally on
>   architectures that support SET_DIRECT_MAP.
>
> The file descriptor backing secret memory mappings is created using a
> dedicated memfd_secret system call The desired protection mode for the
> memory is configured using flags parameter of the system call. The mmap()
> of the file descriptor created with memfd_secret() will create a "secret"
> memory mapping. The pages in that mapping will be marked as not present in
> the direct map and will have desired protection bits set in the user page
> table. For instance, current implementation allows uncached mappings.

I still have serious concerns with uncached mappings.  I'm not saying
I can't be convinced, but I'm not currently convinced that we should
allow user code to create UC mappings on x86.

--Andy

  reply	other threads:[~2020-09-16 18:50 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-16  7:28 Mike Rapoport
2020-09-16 18:49 ` Andy Lutomirski [this message]
2020-09-16  7:35 Mike Rapoport
2020-09-16 23:20 ` Andrew Morton
2020-09-17  5:46   ` Michael Kerrisk (man-pages)
2020-09-17  6:02     ` Mike Rapoport
2020-09-17  6:00   ` Mike Rapoport
2020-09-17 13:27 ` Qian Cai
2020-09-18 18:25   ` Qian Cai
2020-09-21  8:07     ` Stephen Rothwell

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