x86: Drop opt_pku entirely

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.

Visibility of PKU to guests should be handled via its vm.cfg file.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Henry Wang <Henry.Wang@arm.com>

CHANGELOG.md

@@ -25,6 +25,10 @@ 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 was redundant with the unsupported
+   "cpuid=no-pku".  Visibility of PKU to guests should be via its vm.cfg file.
 
 ## [4.17.0](https://xenbits.xen.org/gitweb/?p=xen.git;a=shortlog;h=RELEASE-4.17.0) - 2022-12-12
 

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>`
 

xen/arch/x86/cpu/common.c

@@ -29,10 +29,6 @@ bool __read_mostly opt_dom0_cpuid_faulting = true;
 bool opt_arat = true;
 boolean_param("arat", opt_arat);
 
-/* pku: Flag to enable Memory Protection Keys (default on). */
-static bool opt_pku = true;
-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."