linux-kernel - Re: [PATCH v4 0/3] selftests/lam: get_user additions and LAM enabled check

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Message-ID: <3dnmce4m7cgarq74gev6sbae5djwdqjm44ri4pwl3uhesxfgpk@6srb3wppkeun>
Date: Wed, 27 Nov 2024 14:13:48 +0200
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
Cc: shuah@...nel.org, hpa@...or.com, x86@...nel.org, 
	dave.hansen@...ux.intel.com, bp@...en8.de, mingo@...hat.com, tglx@...utronix.de, 
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v4 0/3] selftests/lam: get_user additions and LAM enabled
 check

On Tue, Nov 26, 2024 at 02:34:47PM +0100, Maciej Wieczor-Retman wrote:
> Recent change in how get_user() handles pointers [1] has a specific case
> for LAM. It assigns a different bitmask that's later used to check
> whether a pointer comes from userland in get_user().
> 
> While currently commented out (until LASS [2] is merged into the kernel)
> it's worth making changes to the LAM selftest ahead of time.
> 
> Modify cpu_has_la57() so it provides current paging level information
> instead of the cpuid one.
> 
> Add test case to LAM that utilizes a ioctl (FIOASYNC) syscall which uses
> get_user() in its implementation. Execute the syscall with differently
> tagged pointers to verify that valid user pointers are passing through
> and invalid kernel/non-canonical pointers are not.
> 
> Also to avoid unhelpful test failures add a check in main() to skip
> running tests if LAM was not compiled into the kernel.
> 
> Code was tested on a Sierra Forest Xeon machine that's LAM capable. The
> test was ran without issues with both the LAM lines from [1] untouched
> and commented out. The test was also ran without issues with LAM_SUP
> both enabled and disabled.
> 
> 4/5 level pagetables code paths were also successfully tested in Simics
> on a 5-level capable machine.
> 
> [1] https://lore.kernel.org/all/20241024013214.129639-1-torvalds@linux-foundation.org/
> [2] https://lore.kernel.org/all/20241028160917.1380714-1-alexander.shishkin@linux.intel.com/
> 
> Maciej Wieczor-Retman (3):
>   selftests/lam: Move cpu_has_la57() to use cpuinfo flag
>   selftests/lam: Skip test if LAM is disabled
>   selftests/lam: Test get_user() LAM pointer handling
> 
>  tools/testing/selftests/x86/lam.c | 122 ++++++++++++++++++++++++++++--
>  1 file changed, 117 insertions(+), 5 deletions(-)

Apart from the nitpick in 1/3, looks good to me:

Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov