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[PATCH 6/7] x86/cpuid: Fix handling of XSAVE dynamic leaves



First, if XSAVE is available in hardware but not visible to the guest, the
dynamic leaves shouldn't be filled in.

Second, 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_compressed_size() to mirror the uncompressed one.  Cross
check it at boot.

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>

v3:
 * Adjust commit message about !XSAVE guests
 * Rebase over boot time cross check
 * Use raw policy
---
 xen/arch/x86/cpuid.c              | 24 ++++++++--------------
 xen/arch/x86/include/asm/xstate.h |  1 +
 xen/arch/x86/xstate.c             | 34 +++++++++++++++++++++++++++++++
 3 files changed, 43 insertions(+), 16 deletions(-)

diff --git a/xen/arch/x86/cpuid.c b/xen/arch/x86/cpuid.c
index 7a38e032146a..a822e80c7ea7 100644
--- a/xen/arch/x86/cpuid.c
+++ b/xen/arch/x86/cpuid.c
@@ -330,23 +330,15 @@ void guest_cpuid(const struct vcpu *v, uint32_t leaf,
     case XSTATE_CPUID:
         switch ( subleaf )
         {
-        case 1:
-            if ( !p->xstate.xsavec && !p->xstate.xsaves )
-                break;
-
-            /*
-             * 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);
-            fallthrough;
         case 0:
-            /*
-             * Read CPUID[0xD,0/1].EBX from hardware.  They vary with enabled
-             * XSTATE, and appropriate XCR0|XSS are in context.
-             */
-            res->b = cpuid_count_ebx(leaf, subleaf);
+            if ( p->basic.xsave )
+                res->b = xstate_uncompressed_size(v->arch.xcr0);
+            break;
+
+        case 1:
+            if ( p->xstate.xsavec )
+                res->b = xstate_compressed_size(v->arch.xcr0 |
+                                                v->arch.msrs->xss.raw);
             break;
         }
         break;
diff --git a/xen/arch/x86/include/asm/xstate.h 
b/xen/arch/x86/include/asm/xstate.h
index bfb66dd766b6..da1d89d2f416 100644
--- a/xen/arch/x86/include/asm/xstate.h
+++ b/xen/arch/x86/include/asm/xstate.h
@@ -109,6 +109,7 @@ 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 xstates);
 
 static inline uint64_t xgetbv(unsigned int index)
 {
diff --git a/xen/arch/x86/xstate.c b/xen/arch/x86/xstate.c
index 1b3153600d9c..7b7f2dcaf651 100644
--- a/xen/arch/x86/xstate.c
+++ b/xen/arch/x86/xstate.c
@@ -621,6 +621,34 @@ unsigned int xstate_uncompressed_size(uint64_t xcr0)
     return size;
 }
 
+unsigned int xstate_compressed_size(uint64_t xstates)
+{
+    unsigned int i, size = XSTATE_AREA_MIN_SIZE;
+
+    if ( xstates == 0 ) /* TODO: clean up paths passing 0 in here. */
+        return 0;
+
+    if ( xstates <= (X86_XCR0_SSE | X86_XCR0_FP) )
+        return size;
+
+    /*
+     * For the compressed size, every component matters.  Some componenets are
+     * rounded up to 64 first.
+     */
+    xstates &= ~(X86_XCR0_SSE | X86_XCR0_FP);
+    for_each_set_bit ( i, &xstates, 63 )
+    {
+        const struct xstate_component *c = &raw_cpu_policy.xstate.comp[i];
+
+        if ( c->align )
+            size = ROUNDUP(size, 64);
+
+        size += c->size;
+    }
+
+    return size;
+}
+
 struct xcheck_state {
     uint64_t states;
     uint32_t uncomp_size;
@@ -683,6 +711,12 @@ static void __init check_new_xstate(struct xcheck_state 
*s, uint64_t new)
                   s->states, &new, hw_size, s->comp_size);
 
         s->comp_size = hw_size;
+
+        xen_size = xstate_compressed_size(s->states);
+
+        if ( xen_size != hw_size )
+            panic("XSTATE 0x%016"PRIx64", compressed hw size %#x != xen size 
%#x\n",
+                  s->states, hw_size, xen_size);
     }
     else
         BUG_ON(hw_size); /* Compressed size reported, but no XSAVEC ? */
-- 
2.30.2




 


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