From: Dave Hansen <dave.hansen@intel.com>
To: ira.weiny@intel.com, Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Dan Williams <dan.j.williams@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>,
Rick Edgecombe <rick.p.edgecombe@intel.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH V8 10/44] Documentation/pkeys: Add initial PKS documentation
Date: Fri, 28 Jan 2022 15:57:52 -0800 [thread overview]
Message-ID: <49195bef-1a3f-447b-3de5-daaefbed8561@intel.com> (raw)
In-Reply-To: <20220127175505.851391-11-ira.weiny@intel.com>
On 1/27/22 09:54, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
>
> Add initial overview and configuration information about PKS.
>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> ---
> Documentation/core-api/protection-keys.rst | 57 ++++++++++++++++++++--
> 1 file changed, 53 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/core-api/protection-keys.rst b/Documentation/core-api/protection-keys.rst
> index 12331db474aa..58670e3ee39e 100644
> --- a/Documentation/core-api/protection-keys.rst
> +++ b/Documentation/core-api/protection-keys.rst
> @@ -12,6 +12,9 @@ PKeys Userspace (PKU) is a feature which is found on Intel's Skylake "Scalable
> Processor" Server CPUs and later. And it will be available in future
> non-server Intel parts and future AMD processors.
>
> +Protection Keys for Supervisor pages (PKS) is available in the SDM since May
> +2020.
I'd just remove this. Folks don't need to know the SDM history. I'd
only talk about it here if they would have a hard time finding it
somehow. Seeing as its in the main SDM, I can't see how that's a problem.
> pkeys work by dedicating 4 previously Reserved bits in each page table entry to
> a "protection key", giving 16 possible keys.
>
> @@ -22,13 +25,20 @@ and Write Disable) for each of 16 keys.
> Being a CPU register, PKRU is inherently thread-local, potentially giving each
> thread a different set of protections from every other thread.
>
> -There are two instructions (RDPKRU/WRPKRU) for reading and writing to the
> -register. The feature is only available in 64-bit mode, even though there is
> +For Userspace (PKU), there are two instructions (RDPKRU/WRPKRU) for reading and
> +writing to the register.
> +
> +For Supervisor (PKS), the register (MSR_IA32_PKRS) is accessible only to the
> +kernel through rdmsr and wrmsr.
> +
> +The feature is only available in 64-bit mode, even though there is
> theoretically space in the PAE PTEs. These permissions are enforced on data
> access only and have no effect on instruction fetches.
>
> -Syscalls
> -========
> +
> +
> +Syscalls for user space keys
> +============================
>
> There are 3 system calls which directly interact with pkeys::
>
> @@ -95,3 +105,42 @@ with a read()::
> The kernel will send a SIGSEGV in both cases, but si_code will be set
> to SEGV_PKERR when violating protection keys versus SEGV_ACCERR when
> the plain mprotect() permissions are violated.
> +
> +
> +Kernel API for PKS support
> +==========================
> +
> +Overview
> +--------
> +
> +Similar to user space pkeys, supervisor pkeys allow additional protections to
> +be defined for a supervisor mappings. Unlike user space pkeys, violations of
> +these protections result in a kernel oops.
> +
> +Supervisor Memory Protection Keys (PKS) is a feature which is found on Intel's
> +Sapphire Rapids (and later) "Scalable Processor" Server CPUs. It will also be
> +available in future non-server Intel parts.
This is a little weird. You've already talked about PKRS and then later
introduce the feature?
Also, perhaps this CPU model bit should just be next to the CPU model
bit about PKU.
> +Also qemu has support as well: https://www.qemu.org/2021/04/30/qemu-6-0-0/
> +
> +Kconfig
> +-------
> +Kernel users intending to use PKS support should depend on
> +ARCH_HAS_SUPERVISOR_PKEYS, and select ARCH_ENABLE_SUPERVISOR_PKEYS to turn on
> +this support within the core.
Maybe this should talk about the Kconfig options a bit more. Maybe even
an example:
config MY_NEW_FEATURE
depends on ARCH_HAS_SUPERVISOR_PKEYS
select ARCH_ENABLE_SUPERVISOR_PKEYS
This will make "MY_NEW_FEATURE" unavailable unless the architecture sets
ARCH_HAS_SUPERVISOR_PKEYS. It also makes it possible for multiple
independent features to "select ARCH_ENABLE_SUPERVISOR_PKEYS". PKS
support will not be compiled into the kernel unless one or more features
selects ARCH_ENABLE_SUPERVISOR_PKEYS.
> +MSR details
> +-----------
> +
> +It should be noted that the underlying WRMSR(MSR_IA32_PKRS) is not serializing
> +but still maintains ordering properties similar to WRPKRU.
s/It should be noted that the underlying //
I'd probably say:
WRMSR is typically an architecturally serializing instruction.
However, WRMSR(MSR_IA32_PKRS) is an exceptions. It is not a
serializing instruction and instead maintains ordering
properties similar to WRPKRU.
and maybe:
Check the WRPKRU documentation in the latest version of the SDM
for details.
> +Older versions of the SDM on PKRS may be wrong with regard to this
> +serialization. The text should be the same as that of WRPKRU. From the WRPKRU
> +text:
> +
> + WRPKRU will never execute transiently. Memory accesses
> + affected by PKRU register will not execute (even transiently)
> + until all prior executions of WRPKRU have completed execution
> + and updated the PKRU register.
I wouldn't go over this. Software has bugs. Documentation has bugs. I
expect folks to use the most recent version.
BTW, there are still a few places in SDM 076 that miss mentioning the
non-serializing properties of PKRS. I also don't see anything
specifically about the speculative behavior. There might be fixes on
the way, but can you double-check?
next prev parent reply other threads:[~2022-01-28 23:57 UTC|newest]
Thread overview: 145+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-27 17:54 [PATCH V8 00/44] PKS/PMEM: Add Stray Write Protection ira.weiny
2022-01-27 17:54 ` [PATCH V8 01/44] entry: Create an internal irqentry_exit_cond_resched() call ira.weiny
2022-01-27 17:54 ` [PATCH V8 02/44] Documentation/protection-keys: Clean up documentation for User Space pkeys ira.weiny
2022-01-28 22:39 ` Dave Hansen
2022-02-01 23:49 ` Ira Weiny
2022-02-01 23:54 ` Dave Hansen
2022-01-27 17:54 ` [PATCH V8 03/44] x86/pkeys: Create pkeys_common.h ira.weiny
2022-01-28 22:43 ` Dave Hansen
2022-02-02 1:00 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 04/44] x86/pkeys: Add additional PKEY helper macros ira.weiny
2022-01-28 22:47 ` Dave Hansen
2022-02-02 20:21 ` Ira Weiny
2022-02-02 20:26 ` Dave Hansen
2022-02-02 20:28 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 05/44] x86/fpu: Refactor arch_set_user_pkey_access() ira.weiny
2022-01-28 22:50 ` Dave Hansen
2022-02-02 20:22 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 06/44] mm/pkeys: Add Kconfig options for PKS ira.weiny
2022-01-28 22:54 ` Dave Hansen
2022-01-28 23:10 ` Ira Weiny
2022-01-28 23:51 ` Dave Hansen
2022-02-04 19:08 ` Ira Weiny
2022-02-09 5:34 ` Ira Weiny
2022-02-14 19:20 ` Dave Hansen
2022-02-14 23:03 ` Ira Weiny
2022-01-29 0:06 ` Dave Hansen
2022-02-04 19:14 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 07/44] x86/pkeys: Add PKS CPU feature bit ira.weiny
2022-01-28 23:05 ` Dave Hansen
2022-02-04 19:21 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 08/44] x86/fault: Adjust WARN_ON for PKey fault ira.weiny
2022-01-28 23:10 ` Dave Hansen
2022-02-04 20:06 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 09/44] x86/pkeys: Enable PKS on cpus which support it ira.weiny
2022-01-28 23:18 ` Dave Hansen
2022-01-28 23:41 ` Ira Weiny
2022-01-28 23:53 ` Dave Hansen
2022-01-27 17:54 ` [PATCH V8 10/44] Documentation/pkeys: Add initial PKS documentation ira.weiny
2022-01-28 23:57 ` Dave Hansen [this message]
2022-01-27 17:54 ` [PATCH V8 11/44] mm/pkeys: Define static PKS key array and default values ira.weiny
2022-01-29 0:02 ` Dave Hansen
2022-02-04 23:54 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 12/44] mm/pkeys: Define PKS page table macros ira.weiny
2022-01-27 17:54 ` [PATCH V8 13/44] mm/pkeys: Add initial PKS Test code ira.weiny
2022-01-31 19:30 ` Edgecombe, Rick P
2022-02-09 23:44 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 14/44] x86/pkeys: Introduce pks_write_pkrs() ira.weiny
2022-01-29 0:12 ` Dave Hansen
2022-01-29 0:16 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 15/44] x86/pkeys: Preserve the PKS MSR on context switch ira.weiny
2022-01-29 0:22 ` Dave Hansen
2022-02-11 6:10 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 16/44] mm/pkeys: Introduce pks_mk_readwrite() ira.weiny
2022-01-31 23:10 ` Edgecombe, Rick P
2022-02-18 2:22 ` Ira Weiny
2022-02-01 17:40 ` Dave Hansen
2022-02-18 4:39 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 17/44] mm/pkeys: Introduce pks_mk_noaccess() ira.weiny
2022-01-27 17:54 ` [PATCH V8 18/44] x86/fault: Add a PKS test fault hook ira.weiny
2022-01-31 19:56 ` Edgecombe, Rick P
2022-02-11 20:40 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 19/44] mm/pkeys: PKS Testing, add pks_mk_*() tests ira.weiny
2022-02-01 17:45 ` Dave Hansen
2022-02-18 5:34 ` Ira Weiny
2022-02-18 15:28 ` Dave Hansen
2022-02-18 17:25 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 20/44] mm/pkeys: Add PKS test for context switching ira.weiny
2022-02-01 17:43 ` Edgecombe, Rick P
2022-02-22 21:42 ` Ira Weiny
2022-02-01 17:47 ` Edgecombe, Rick P
2022-02-01 19:52 ` Edgecombe, Rick P
2022-02-18 6:03 ` Ira Weiny
2022-02-18 6:02 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 21/44] x86/entry: Add auxiliary pt_regs space ira.weiny
2022-01-27 17:54 ` [PATCH V8 22/44] entry: Pass pt_regs to irqentry_exit_cond_resched() ira.weiny
2022-01-27 17:54 ` [PATCH V8 23/44] entry: Add architecture auxiliary pt_regs save/restore calls ira.weiny
2022-01-27 17:54 ` [PATCH V8 24/44] x86/entry: Define arch_{save|restore}_auxiliary_pt_regs() ira.weiny
2022-01-27 17:54 ` [PATCH V8 25/44] x86/pkeys: Preserve PKRS MSR across exceptions ira.weiny
2022-01-27 17:54 ` [PATCH V8 26/44] x86/fault: Print PKS MSR on fault ira.weiny
2022-02-01 18:13 ` Edgecombe, Rick P
2022-02-18 6:01 ` Ira Weiny
2022-02-18 17:28 ` Edgecombe, Rick P
2022-02-18 20:20 ` Dave Hansen
2022-02-18 20:54 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 27/44] mm/pkeys: Add PKS exception test ira.weiny
2022-01-27 17:54 ` [PATCH V8 28/44] mm/pkeys: Introduce pks_update_exception() ira.weiny
2022-01-27 17:54 ` [PATCH V8 29/44] mm/pkeys: Introduce PKS fault callbacks ira.weiny
2022-01-27 17:54 ` [PATCH V8 30/44] mm/pkeys: Test setting a PKS key in a custom fault callback ira.weiny
2022-02-01 0:55 ` Edgecombe, Rick P
2022-03-01 15:39 ` Ira Weiny
2022-02-01 17:42 ` Edgecombe, Rick P
2022-02-11 20:44 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 31/44] mm/pkeys: Add pks_available() ira.weiny
2022-01-27 17:54 ` [PATCH V8 32/44] memremap_pages: Add Kconfig for DEVMAP_ACCESS_PROTECTION ira.weiny
2022-02-04 15:49 ` Dan Williams
2022-01-27 17:54 ` [PATCH V8 33/44] memremap_pages: Introduce pgmap_protection_available() ira.weiny
2022-02-04 16:19 ` Dan Williams
2022-02-28 16:59 ` Ira Weiny
2022-03-01 15:56 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 34/44] memremap_pages: Introduce a PGMAP_PROTECTION flag ira.weiny
2022-01-27 17:54 ` [PATCH V8 35/44] memremap_pages: Introduce devmap_protected() ira.weiny
2022-01-27 17:54 ` [PATCH V8 36/44] memremap_pages: Reserve a PKS PKey for eventual use by PMEM ira.weiny
2022-02-01 18:35 ` Edgecombe, Rick P
2022-02-04 17:12 ` Dan Williams
2022-02-05 5:40 ` Ira Weiny
2022-02-05 8:19 ` Dan Williams
2022-02-06 18:14 ` Dan Williams
2022-02-08 22:48 ` Ira Weiny
2022-02-08 23:22 ` Dan Williams
2022-02-08 23:42 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 37/44] memremap_pages: Set PKS PKey in PTEs if PGMAP_PROTECTIONS is requested ira.weiny
2022-02-04 17:41 ` Dan Williams
2022-03-01 18:15 ` Ira Weiny
2022-01-27 17:54 ` [PATCH V8 38/44] memremap_pages: Define pgmap_mk_{readwrite|noaccess}() calls ira.weiny
2022-02-04 18:35 ` Dan Williams
2022-02-05 0:09 ` Ira Weiny
2022-02-05 0:19 ` Dan Williams
2022-02-05 0:25 ` Dan Williams
2022-02-05 0:27 ` Dan Williams
2022-02-05 5:55 ` Ira Weiny
2022-02-05 6:28 ` Dan Williams
2022-02-22 22:05 ` Ira Weiny
2022-01-27 17:55 ` [PATCH V8 39/44] memremap_pages: Add memremap.pks_fault_mode ira.weiny
2022-02-01 1:16 ` Edgecombe, Rick P
2022-03-02 0:20 ` Ira Weiny
2022-02-04 19:01 ` Dan Williams
2022-03-02 2:00 ` Ira Weiny
2022-01-27 17:55 ` [PATCH V8 40/44] memremap_pages: Add pgmap_protection_flag_invalid() ira.weiny
2022-02-01 1:37 ` Edgecombe, Rick P
2022-03-02 2:01 ` Ira Weiny
2022-02-04 19:18 ` Dan Williams
2022-01-27 17:55 ` [PATCH V8 41/44] kmap: Ensure kmap works for devmap pages ira.weiny
2022-02-04 21:07 ` Dan Williams
2022-03-01 19:45 ` Ira Weiny
2022-03-01 19:50 ` Ira Weiny
2022-03-01 20:05 ` Dan Williams
2022-03-01 23:03 ` Ira Weiny
2022-01-27 17:55 ` [PATCH V8 42/44] dax: Stray access protection for dax_direct_access() ira.weiny
2022-02-04 5:19 ` Dan Williams
2022-03-01 18:13 ` Ira Weiny
2022-01-27 17:55 ` [PATCH V8 43/44] nvdimm/pmem: Enable stray access protection ira.weiny
2022-02-04 21:10 ` Dan Williams
2022-03-01 18:18 ` Ira Weiny
2022-01-27 17:55 ` [PATCH V8 44/44] devdax: " ira.weiny
2022-02-04 21:12 ` Dan Williams
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