[PATCH v2 8/8] x86/hvm: Support PKS for HAP guests

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

With all infrastructure in place, advertise the PKS CPUID bit to HAP guests,
and let them set CR4.PKS.

Experiment with a tweak to the layout of hvm_cr4_guest_valid_bits() so future
additions will be just a single added line.

The current context switching behaviour is tied to how VT-x works, so leave a
safety check in the short term.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
---
 xen/arch/x86/cpuid.c                        | 9 +++++++++
 xen/arch/x86/hvm/hvm.c                      | 4 +++-
 xen/include/public/arch-x86/cpufeatureset.h | 2 +-
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/cpuid.c b/xen/arch/x86/cpuid.c
index acc2f606cea8..b22725c492e7 100644
--- a/xen/arch/x86/cpuid.c
+++ b/xen/arch/x86/cpuid.c
@@ -579,6 +579,15 @@ static void __init calculate_hvm_max_policy(void)
             __clear_bit(X86_FEATURE_XSAVES, hvm_featureset);
     }
 
+    /*
+     * Xen doesn't use PKS, so the guest support for it has opted to not use
+     * the VMCS load/save controls for efficiency reasons.  This depends on
+     * the exact vmentry/exit behaviour, so don't expose PKS in other
+     * situations until someone has cross-checked the behaviour for safety.
+     */
+    if ( !cpu_has_vmx )
+        __clear_bit(X86_FEATURE_PKS, hvm_featureset);
+
     guest_common_feature_adjustments(hvm_featureset);
 
     sanitise_featureset(hvm_featureset);
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index c6c1eea18003..606f0e864981 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -969,7 +969,9 @@ unsigned long hvm_cr4_guest_valid_bits(const struct domain 
*d)
             (p->feat.smep     ? X86_CR4_SMEP              : 0) |
             (p->feat.smap     ? X86_CR4_SMAP              : 0) |
             (p->feat.pku      ? X86_CR4_PKE               : 0) |
-            (cet              ? X86_CR4_CET               : 0));
+            (cet              ? X86_CR4_CET               : 0) |
+            (p->feat.pks      ? X86_CR4_PKS               : 0) |
+            0);
 }
 
 static int cf_check hvm_load_cpu_ctxt(struct domain *d, hvm_domain_context_t 
*h)
diff --git a/xen/include/public/arch-x86/cpufeatureset.h 
b/xen/include/public/arch-x86/cpufeatureset.h
index 5444bc5d8374..3b85bcca1537 100644
--- a/xen/include/public/arch-x86/cpufeatureset.h
+++ b/xen/include/public/arch-x86/cpufeatureset.h
@@ -227,7 +227,7 @@ XEN_CPUFEATURE(CLDEMOTE,      6*32+25) /*A  CLDEMOTE 
instruction */
 XEN_CPUFEATURE(MOVDIRI,       6*32+27) /*a  MOVDIRI instruction */
 XEN_CPUFEATURE(MOVDIR64B,     6*32+28) /*a  MOVDIR64B instruction */
 XEN_CPUFEATURE(ENQCMD,        6*32+29) /*   ENQCMD{,S} instructions */
-XEN_CPUFEATURE(PKS,           6*32+31) /*   Protection Key for Supervisor */
+XEN_CPUFEATURE(PKS,           6*32+31) /*H  Protection Key for Supervisor */
 
 /* AMD-defined CPU features, CPUID level 0x80000007.edx, word 7 */
 XEN_CPUFEATURE(HW_PSTATE,     7*32+ 7) /*   Hardware Pstates */
-- 
2.11.0