[PATCH] x86: Drop opt_pku entirely

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

This option is particularly dubious as Xen does not use Protection Keys, owing
to the sharing of pagetables with PV guests.  All this option does is hide PKU
by default from HVM guests, and is therefore redundant with the more generic
cpuid=no-pku.

The variable ought to be in __initdata given it's single user, but deleting it
entirely looks to be a better course of action.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Henry Wang <Henry.Wang@xxxxxxx>
---
 CHANGELOG.md                      |  3 +++
 docs/misc/xen-command-line.pandoc | 10 ----------
 xen/arch/x86/cpu/common.c         |  7 -------
 3 files changed, 3 insertions(+), 17 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7d7e0590f8c6..43f15dc34cbf 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,9 @@ The format is based on [Keep a 
Changelog](https://keepachangelog.com/en/1.0.0/)
  - Add support for AVX512-FP16 on x86.
  - On Arm, Xen supports guests running SVE/SVE2 instructions. (Tech Preview)
 
+### Removed
+ - On x86, the "pku" command line option has been removed.  It has never
+   behaved precisely as described, and redundant with "cpuid=no-pku".
 
 ## 
[4.17.0](https://xenbits.xen.org/gitweb/?p=xen.git;a=shortlog;h=RELEASE-4.17.0) 
- 2022-12-12
 
diff --git a/docs/misc/xen-command-line.pandoc 
b/docs/misc/xen-command-line.pandoc
index 4060ebdc5d76..9d66688bd1ff 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -1950,16 +1950,6 @@ for all of them (`true`), only for those subject to XPTI 
(`xpti`) or for
 those not subject to XPTI (`no-xpti`). The feature is used only in case
 INVPCID is supported and not disabled via `invpcid=false`.
 
-### pku (x86)
-> `= <boolean>`
-
-> Default: `true`
-
-Flag to enable Memory Protection Keys.
-
-The protection-key feature provides an additional mechanism by which IA-32e
-paging controls access to usermode addresses.
-
 ### ple_gap
 > `= <integer>`
 
diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index cfcdaace125b..14021ffc66d8 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -29,10 +29,6 @@ bool __read_mostly opt_dom0_cpuid_faulting = true;
 bool_t opt_arat = 1;
 boolean_param("arat", opt_arat);
 
-/* pku: Flag to enable Memory Protection Keys (default on). */
-static bool_t opt_pku = 1;
-boolean_param("pku", opt_pku);
-
 unsigned int opt_cpuid_mask_ecx = ~0u;
 integer_param("cpuid_mask_ecx", opt_cpuid_mask_ecx);
 unsigned int opt_cpuid_mask_edx = ~0u;
@@ -522,9 +518,6 @@ void identify_cpu(struct cpuinfo_x86 *c)
                this_cpu->c_init(c);
 
 
-       if (c == &boot_cpu_data && !opt_pku)
-               setup_clear_cpu_cap(X86_FEATURE_PKU);
-
        /*
         * The vendor-specific functions might have changed features.  Now
         * we do "generic changes."
-- 
2.30.2