[PATCH v4 5/7] x86/cpu-policy: Simplify recalculate_xstate()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Make use of xstate_uncompressed_size() helper rather than maintaining the
running calculation while accumulating feature components.

The rest of the CPUID data can come direct from the raw cpu policy.  All
per-component data form an ABI through the behaviour of the X{SAVE,RSTOR}*
instructions.

Use for_each_set_bit() rather than opencoding a slightly awkward version of
it.  Mask the attributes in ecx down based on the visible features.  This
isn't actually necessary for any components or attributes defined at the time
of writing (up to AMX), but is added out of an abundance of caution.

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: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>

v2:
 * Tie ALIGN64 to xsavec rather than xsaves.
v3:
 * Tweak commit message.
---
 xen/arch/x86/cpu-policy.c         | 55 +++++++++++--------------------
 xen/arch/x86/include/asm/xstate.h |  1 +
 2 files changed, 21 insertions(+), 35 deletions(-)

diff --git a/xen/arch/x86/cpu-policy.c b/xen/arch/x86/cpu-policy.c
index 5b66f002df05..304dc20cfab8 100644
--- a/xen/arch/x86/cpu-policy.c
+++ b/xen/arch/x86/cpu-policy.c
@@ -193,8 +193,7 @@ static void sanitise_featureset(uint32_t *fs)
 static void recalculate_xstate(struct cpu_policy *p)
 {
     uint64_t xstates = XSTATE_FP_SSE;
-    uint32_t xstate_size = XSTATE_AREA_MIN_SIZE;
-    unsigned int i, Da1 = p->xstate.Da1;
+    unsigned int i, ecx_mask = 0, Da1 = p->xstate.Da1;
 
     /*
      * The Da1 leaf is the only piece of information preserved in the common
@@ -206,61 +205,47 @@ static void recalculate_xstate(struct cpu_policy *p)
         return;
 
     if ( p->basic.avx )
-    {
         xstates |= X86_XCR0_YMM;
-        xstate_size = max(xstate_size,
-                          xstate_offsets[X86_XCR0_YMM_POS] +
-                          xstate_sizes[X86_XCR0_YMM_POS]);
-    }
 
     if ( p->feat.mpx )
-    {
         xstates |= X86_XCR0_BNDREGS | X86_XCR0_BNDCSR;
-        xstate_size = max(xstate_size,
-                          xstate_offsets[X86_XCR0_BNDCSR_POS] +
-                          xstate_sizes[X86_XCR0_BNDCSR_POS]);
-    }
 
     if ( p->feat.avx512f )
-    {
         xstates |= X86_XCR0_OPMASK | X86_XCR0_ZMM | X86_XCR0_HI_ZMM;
-        xstate_size = max(xstate_size,
-                          xstate_offsets[X86_XCR0_HI_ZMM_POS] +
-                          xstate_sizes[X86_XCR0_HI_ZMM_POS]);
-    }
 
     if ( p->feat.pku )
-    {
         xstates |= X86_XCR0_PKRU;
-        xstate_size = max(xstate_size,
-                          xstate_offsets[X86_XCR0_PKRU_POS] +
-                          xstate_sizes[X86_XCR0_PKRU_POS]);
-    }
 
-    p->xstate.max_size  =  xstate_size;
+    /* Subleaf 0 */
+    p->xstate.max_size =
+        xstate_uncompressed_size(xstates & ~XSTATE_XSAVES_ONLY);
     p->xstate.xcr0_low  =  xstates & ~XSTATE_XSAVES_ONLY;
     p->xstate.xcr0_high = (xstates & ~XSTATE_XSAVES_ONLY) >> 32;
 
+    /* Subleaf 1 */
     p->xstate.Da1 = Da1;
+    if ( p->xstate.xsavec )
+        ecx_mask |= XSTATE_ALIGN64;
+
     if ( p->xstate.xsaves )
     {
+        ecx_mask |= XSTATE_XSS;
         p->xstate.xss_low   =  xstates & XSTATE_XSAVES_ONLY;
         p->xstate.xss_high  = (xstates & XSTATE_XSAVES_ONLY) >> 32;
     }
-    else
-        xstates &= ~XSTATE_XSAVES_ONLY;
 
-    for ( i = 2; i < min(63UL, ARRAY_SIZE(p->xstate.comp)); ++i )
+    /* Subleafs 2+ */
+    xstates &= ~XSTATE_FP_SSE;
+    BUILD_BUG_ON(ARRAY_SIZE(p->xstate.comp) < 63);
+    for_each_set_bit ( i, &xstates, 63 )
     {
-        uint64_t curr_xstate = 1UL << i;
-
-        if ( !(xstates & curr_xstate) )
-            continue;
-
-        p->xstate.comp[i].size   = xstate_sizes[i];
-        p->xstate.comp[i].offset = xstate_offsets[i];
-        p->xstate.comp[i].xss    = curr_xstate & XSTATE_XSAVES_ONLY;
-        p->xstate.comp[i].align  = curr_xstate & xstate_align;
+        /*
+         * Pass through size (eax) and offset (ebx) directly.  Visbility of
+         * attributes in ecx limited by visible features in Da1.
+         */
+        p->xstate.raw[i].a = raw_cpu_policy.xstate.raw[i].a;
+        p->xstate.raw[i].b = raw_cpu_policy.xstate.raw[i].b;
+        p->xstate.raw[i].c = raw_cpu_policy.xstate.raw[i].c & ecx_mask;
     }
 }
 
diff --git a/xen/arch/x86/include/asm/xstate.h 
b/xen/arch/x86/include/asm/xstate.h
index f5115199d4f9..bfb66dd766b6 100644
--- a/xen/arch/x86/include/asm/xstate.h
+++ b/xen/arch/x86/include/asm/xstate.h
@@ -40,6 +40,7 @@ extern uint32_t mxcsr_mask;
 #define XSTATE_XSAVES_ONLY         0
 #define XSTATE_COMPACTION_ENABLED  (1ULL << 63)
 
+#define XSTATE_XSS     (1U << 0)
 #define XSTATE_ALIGN64 (1U << 1)
 
 extern u64 xfeature_mask;
-- 
2.39.2