linux-kernel - Re: [PATCH 1/6] arm64/vdso: use the fault callback to map vvar pages

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Message-ID: <20200727064545.GA9619@gmail.com>
Date:   Sun, 26 Jul 2020 23:45:45 -0700
From:   Andrei Vagin <avagin@...il.com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Dmitry Safonov <dima@...sta.com>
Subject: Re: [PATCH 1/6] arm64/vdso: use the fault callback to map vvar pages

On Fri, Jul 24, 2020 at 06:26:23PM +0100, Catalin Marinas wrote:
> On Wed, 24 Jun 2020 01:33:16 -0700, Andrei Vagin wrote:
> > Currently the vdso has no awareness of time namespaces, which may
> > apply distinct offsets to processes in different namespaces. To handle
> > this within the vdso, we'll need to expose a per-namespace data page.
> > 
> > As a preparatory step, this patch separates the vdso data page from
> > the code pages, and has it faulted in via its own fault callback.
> > Subsquent patches will extend this to support distinct pages per time
> > namespace.
> > 
> > [...]
> 
> Applied to arm64 (for-next/timens), provisionally.
> 
> One potential issue I did not check is the compat vDSO. The arm32 port
> does not support timens currently. IIUC, with these patches and
> COMPAT_VDSO enabled, it will allow timens for compat processes. Normally
> I'd like the arm32 support first before updating compat but I don't
> think there would be any interface incompatibility here.
> 
> However, does this still work for arm32 processes if COMPAT_VDSO is
> disabled in the arm64 kernel?

Yes, it does. I checked that the timens test passes with and without
COMPAT_VDSO:

[avagin@...top linux]$ git describe HEAD
v5.8-rc3-6-g9614cc576d76

alpine:/tip/tools/testing/selftests/timens# readelf  -h ./timens
ELF Header:
  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF32
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              DYN (Shared object file)
  Machine:                           ARM
  Version:                           0x1
  Entry point address:               0x711
  Start of program headers:          52 (bytes into file)
  Start of section headers:          15444 (bytes into file)
  Flags:                             0x5000400, Version5 EABI,
hard-float ABI
  Size of this header:               52 (bytes)
  Size of program headers:           32 (bytes)
  Number of program headers:         7
  Size of section headers:           40 (bytes)
  Number of section headers:         32
  Section header string table index: 31

alpine:/tip/tools/testing/selftests/timens# uname -a
Linux arm64-alpine 5.8.0-rc3+ #100 SMP Sun Jul 26 23:21:07 PDT 2020
aarch64 Linux


[avagin@...top linux]$ cat  .config | grep VDSO
CONFIG_COMPAT_VDSO=y
CONFIG_THUMB2_COMPAT_VDSO=y
CONFIG_HAVE_GENERIC_VDSO=y
CONFIG_GENERIC_COMPAT_VDSO=y
CONFIG_GENERIC_VDSO_TIME_NS=y


alpine:/tip/tools/testing/selftests/timens# ./timens
1..10
ok 1 Passed for CLOCK_BOOTTIME (syscall)
ok 2 Passed for CLOCK_BOOTTIME (vdso)
not ok 3 # SKIP CLOCK_BOOTTIME_ALARM isn't supported
not ok 4 # SKIP CLOCK_BOOTTIME_ALARM isn't supported
ok 5 Passed for CLOCK_MONOTONIC (syscall)
ok 6 Passed for CLOCK_MONOTONIC (vdso)
ok 7 Passed for CLOCK_MONOTONIC_COARSE (syscall)
ok 8 Passed for CLOCK_MONOTONIC_COARSE (vdso)
ok 9 Passed for CLOCK_MONOTONIC_RAW (syscall)
ok 10 Passed for CLOCK_MONOTONIC_RAW (vdso)
# Pass 8 Fail 0 Xfail 0 Xpass 0 Skip 2 Error 0


[avagin@...top linux]$ cat  .config | grep VDSO
# CONFIG_COMPAT_VDSO is not set
CONFIG_HAVE_GENERIC_VDSO=y
CONFIG_GENERIC_VDSO_TIME_NS=y

alpine:/tip/tools/testing/selftests/timens# ./timens
1..10
ok 1 Passed for CLOCK_BOOTTIME (syscall)
ok 2 Passed for CLOCK_BOOTTIME (vdso)
not ok 3 # SKIP CLOCK_BOOTTIME_ALARM isn't supported
not ok 4 # SKIP CLOCK_BOOTTIME_ALARM isn't supported
ok 5 Passed for CLOCK_MONOTONIC (syscall)
ok 6 Passed for CLOCK_MONOTONIC (vdso)
ok 7 Passed for CLOCK_MONOTONIC_COARSE (syscall)
ok 8 Passed for CLOCK_MONOTONIC_COARSE (vdso)
ok 9 Passed for CLOCK_MONOTONIC_RAW (syscall)
ok 10 Passed for CLOCK_MONOTONIC_RAW (vdso)
# Pass 8 Fail 0 Xfail 0 Xpass 0 Skip 2 Error 0

Thanks,
Andrei