[PATCH 5/5] x86/cpuid: Fix handling of xsave dynamic leaves

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

If max leaf is greater than 0xd but xsave not available to the guest, then the
current XSAVE size should not be filled in.  This is a latent bug for now as
the guest max leaf is 0xd, but will become problematic in the future.

The comment concerning XSS state is wrong.  VT-x doesn't manage host/guest
state automatically, but there is provision for "host only" bits to be set, so
the implications are still accurate.

Introduce {xstate,hw}_compressed_size() helpers to mirror the uncompressed
ones.

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>
---
 xen/arch/x86/cpuid.c         | 23 +++++++--------------
 xen/arch/x86/xstate.c        | 49 ++++++++++++++++++++++++++++++++++++++++++++
 xen/include/asm-x86/xstate.h |  1 +
 3 files changed, 57 insertions(+), 16 deletions(-)

diff --git a/xen/arch/x86/cpuid.c b/xen/arch/x86/cpuid.c
index c7f8388e5d..92745aa63f 100644
--- a/xen/arch/x86/cpuid.c
+++ b/xen/arch/x86/cpuid.c
@@ -1041,24 +1041,15 @@ void guest_cpuid(const struct vcpu *v, uint32_t leaf,
     case XSTATE_CPUID:
         switch ( subleaf )
         {
+        case 0:
+            if ( p->basic.xsave )
+                res->b = xstate_uncompressed_size(v->arch.xcr0);
+            break;
+
         case 1:
             if ( p->xstate.xsaves )
-            {
-                /*
-                 * TODO: Figure out what to do for XSS state.  VT-x manages
-                 * host vs guest MSR_XSS automatically, so as soon as we start
-                 * supporting any XSS states, the wrong XSS will be in
-                 * context.
-                 */
-                BUILD_BUG_ON(XSTATE_XSAVES_ONLY != 0);
-
-                /*
-                 * Read CPUID[0xD,0/1].EBX from hardware.  They vary with
-                 * enabled XSTATE, and appropraite XCR0|XSS are in context.
-                 */
-        case 0:
-                res->b = cpuid_count_ebx(leaf, subleaf);
-            }
+                res->b = xstate_compressed_size(v->arch.xcr0 |
+                                                v->arch.msrs->xss.raw);
             break;
         }
         break;
diff --git a/xen/arch/x86/xstate.c b/xen/arch/x86/xstate.c
index d4c01da574..03489f0cf4 100644
--- a/xen/arch/x86/xstate.c
+++ b/xen/arch/x86/xstate.c
@@ -602,6 +602,55 @@ unsigned int xstate_uncompressed_size(uint64_t xcr0)
     return size;
 }
 
+static unsigned int hw_compressed_size(uint64_t xstates)
+{
+    uint64_t curr_xcr0 = get_xcr0(), curr_xss = get_msr_xss();
+    unsigned int size;
+    bool ok;
+
+    ok = set_xcr0(xstates & ~XSTATE_XSAVES_ONLY);
+    ASSERT(ok);
+    set_msr_xss(xstates & XSTATE_XSAVES_ONLY);
+
+    size = cpuid_count_ebx(XSTATE_CPUID, 1);
+
+    ok = set_xcr0(curr_xcr0);
+    ASSERT(ok);
+    set_msr_xss(curr_xss);
+
+    return size;
+}
+
+unsigned int xstate_compressed_size(uint64_t xstates)
+{
+    unsigned int i, size = XSTATE_AREA_MIN_SIZE;
+
+    xstates &= ~XSTATE_FP_SSE;
+    for_each_set_bit ( i, &xstates, 63 )
+    {
+        if ( test_bit(i, &xstate_align) )
+            size = ROUNDUP(size, 64);
+
+        size += xstate_sizes[i];
+    }
+
+    /* In debug builds, cross-check our calculation with hardware. */
+    if ( IS_ENABLED(CONFIG_DEBUG) )
+    {
+        unsigned int hwsize;
+
+        xstates |= XSTATE_FP_SSE;
+        hwsize = hw_compressed_size(xstates);
+
+        if ( size != hwsize )
+            printk_once(XENLOG_ERR "%s(%#"PRIx64") size %#x != hwsize %#x\n",
+                        __func__, xstates, size, hwsize);
+        size = hwsize;
+    }
+
+    return size;
+}
+
 /* Collect the information of processor's extended state */
 void xstate_init(struct cpuinfo_x86 *c)
 {
diff --git a/xen/include/asm-x86/xstate.h b/xen/include/asm-x86/xstate.h
index 02d6f171b8..ecf7bbc5cd 100644
--- a/xen/include/asm-x86/xstate.h
+++ b/xen/include/asm-x86/xstate.h
@@ -108,6 +108,7 @@ void xstate_free_save_area(struct vcpu *v);
 int xstate_alloc_save_area(struct vcpu *v);
 void xstate_init(struct cpuinfo_x86 *c);
 unsigned int xstate_uncompressed_size(uint64_t xcr0);
+unsigned int xstate_compressed_size(uint64_t states);
 
 static inline uint64_t xgetbv(unsigned int index)
 {
-- 
2.11.0