[Xen-devel] [PATCH v6 1/4] xen/libxc: Allow changing max number of hypervisor cpuid leaves

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

Add support for changing max number of hypervisor leaves from configuration
file.

This number can be specified using xl's standard 'cpuid' option. Only lowest
8 bits of leaf's 0x40000x00 eax register are processed, all others are ignored.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
 tools/libxc/xc_cpuid_x86.c |   11 +++++++++++
 xen/arch/x86/traps.c       |   18 ++++++++++++------
 2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/tools/libxc/xc_cpuid_x86.c b/tools/libxc/xc_cpuid_x86.c
index bbbf9b8..21ba68b 100644
--- a/tools/libxc/xc_cpuid_x86.c
+++ b/tools/libxc/xc_cpuid_x86.c
@@ -555,6 +555,17 @@ static int xc_cpuid_policy(
 {
     xc_dominfo_t        info;
 
+    /*
+     * For hypervisor leaves (0x4000XXXX) only 0x40000x00.EAX[7:0] bits (max
+     * number of leaves) can be set by user. Hypervisor will enforce this so
+     * all other bits are don't-care and we can set them to zero.
+     */
+    if ( (input[0] & 0xffff0000) == 0x40000000 )
+    {
+        regs[0] = regs[1] = regs[2] = regs[3] = 0;
+        return 0;
+    }
+
     if ( xc_domain_getinfo(xch, domid, 1, &info) == 0 )
         return -EINVAL;
 
diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index c462317..65c34f3 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -677,15 +677,21 @@ int cpuid_hypervisor_leaves( uint32_t idx, uint32_t 
sub_idx,
     struct domain *d = current->domain;
     /* Optionally shift out of the way of Viridian architectural leaves. */
     uint32_t base = is_viridian_domain(d) ? 0x40000100 : 0x40000000;
-    uint32_t limit;
+    uint32_t limit, dummy;
 
     idx -= base;
+    if ( idx > 3 )
+        return 0; /* Avoid unnecessary pass through domain_cpuid() */
 
-    /*
-     * Some Solaris PV drivers fail if max > base + 2. Help them out by
-     * hiding the PVRDTSCP leaf if PVRDTSCP is disabled.
-     */
-    limit = (d->arch.tsc_mode < TSC_MODE_PVRDTSCP) ? 2 : 3;
+    /* Number of leaves may be user-specified */
+    domain_cpuid(d, base, 0, &limit, &dummy, &dummy, &dummy);
+    limit &= 0xff;
+    if ( (limit < 2) || (limit > 3) )
+        /*
+         * Some Solaris PV drivers fail if max > base + 2. Help them out by
+         * hiding the PVRDTSCP leaf if PVRDTSCP is disabled.
+         */
+        limit = (d->arch.tsc_mode < TSC_MODE_PVRDTSCP) ? 2 : 3;
 
     if ( idx > limit ) 
         return 0;
-- 
1.7.10.4


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