[xen staging] xen/arm: create a cpuinfo structure for guest

[patchbot@xxxxxxx]

commit 3669a1cb95983dc1c01be46e7df5dd9357d7b973
Author:     Bertrand Marquis <bertrand.marquis@xxxxxxx>
AuthorDate: Thu Dec 17 15:38:04 2020 +0000
Commit:     Stefano Stabellini <sstabellini@xxxxxxxxxx>
CommitDate: Mon Jan 4 11:25:03 2021 -0800

    xen/arm: create a cpuinfo structure for guest
    
    Create a cpuinfo structure for guest and mask into it the features that
    we do not support in Xen or that we do not want to publish to guests.
    
    Modify some values in the cpuinfo structure for guests to mask some
    features which we do not want to allow to guests (like AMU) or we do not
    support (like SVE).
    Modify some values in the guest cpuinfo structure to guests to hide some
    processor features:
    - SVE as this is not supported by Xen and guest are not allowed to use
    this features (ZEN is set to 0 in CPTR_EL2).
    - AMU as HCPTR_TAM is set in CPTR_EL2 so AMU cannot be used by guests
    All other bits are left untouched.
    - RAS as this is not supported by Xen.
    
    The code is trying to group together registers modifications for the
    same feature to be able in the long term to easily enable/disable a
    feature depending on user parameters or add other registers modification
    in the same place (like enabling/disabling HCR bits).
    
    Signed-off-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 xen/arch/arm/cpufeature.c        | 51 ++++++++++++++++++++++++++++++++++++++++
 xen/include/asm-arm/cpufeature.h |  2 ++
 2 files changed, 53 insertions(+)

diff --git a/xen/arch/arm/cpufeature.c b/xen/arch/arm/cpufeature.c
index 86b99ee960..1f6a85aafe 100644
--- a/xen/arch/arm/cpufeature.c
+++ b/xen/arch/arm/cpufeature.c
@@ -24,6 +24,8 @@
 
 DECLARE_BITMAP(cpu_hwcaps, ARM_NCAPS);
 
+struct cpuinfo_arm __read_mostly guest_cpuinfo;
+
 void update_cpu_capabilities(const struct arm_cpu_capabilities *caps,
                              const char *info)
 {
@@ -151,6 +153,55 @@ void identify_cpu(struct cpuinfo_arm *c)
         c->mvfr.bits[2] = READ_SYSREG(MVFR2_EL1);
 }
 
+/*
+ * This function is creating a cpuinfo structure with values modified to mask
+ * all cpu features that should not be published to guest.
+ * The created structure is then used to provide ID registers values to guests.
+ */
+static int __init create_guest_cpuinfo(void)
+{
+    /*
+     * TODO: The code is currently using only the features detected on the boot
+     * core. In the long term we should try to compute values containing only
+     * features supported by all cores.
+     */
+    guest_cpuinfo = boot_cpu_data;
+
+#ifdef CONFIG_ARM_64
+    /* Hide MPAM support as xen does not support it */
+    guest_cpuinfo.pfr64.mpam = 0;
+    guest_cpuinfo.pfr64.mpam_frac = 0;
+
+    /* Hide SVE as Xen does not support it */
+    guest_cpuinfo.pfr64.sve = 0;
+    guest_cpuinfo.zfr64.bits[0] = 0;
+
+    /* Hide MTE support as Xen does not support it */
+    guest_cpuinfo.pfr64.mte = 0;
+#endif
+
+    /* Hide AMU support */
+#ifdef CONFIG_ARM_64
+    guest_cpuinfo.pfr64.amu = 0;
+#endif
+    guest_cpuinfo.pfr32.amu = 0;
+
+    /* Hide RAS support as Xen does not support it */
+#ifdef CONFIG_ARM_64
+    guest_cpuinfo.pfr64.ras = 0;
+    guest_cpuinfo.pfr64.ras_frac = 0;
+#endif
+    guest_cpuinfo.pfr32.ras = 0;
+    guest_cpuinfo.pfr32.ras_frac = 0;
+
+    return 0;
+}
+/*
+ * This function needs to be run after all smp are started to have
+ * cpuinfo structures for all cores.
+ */
+__initcall(create_guest_cpuinfo);
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/include/asm-arm/cpufeature.h b/xen/include/asm-arm/cpufeature.h
index 74139be1cc..6058744c18 100644
--- a/xen/include/asm-arm/cpufeature.h
+++ b/xen/include/asm-arm/cpufeature.h
@@ -283,6 +283,8 @@ extern void identify_cpu(struct cpuinfo_arm *);
 extern struct cpuinfo_arm cpu_data[];
 #define current_cpu_data cpu_data[smp_processor_id()]
 
+extern struct cpuinfo_arm guest_cpuinfo;
+
 #endif /* __ASSEMBLY__ */
 
 #endif
--
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