[Xen-devel] [PATCH 1/6] x86emul: generalize wbinvd() hook

[Jan Beulich <JBeulich@xxxxxxxx>]

The hook is already in use for other purposes, and emulating e.g.
CLFLUSH by issuing WBINVD is, well, not very nice. Rename the hook and
add parameters. Use lighter weight flushing insns when possible in
hvmemul_cache_op().

hvmemul_cache_op() treating x86emul_invd the same as x86emul_wbinvd is
to retain original behavior, but I'm not sure this is what we want in
the long run.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Use cache_op() as hook name. Convert macros to inline functions in
     system.h. Re-base.
---
I was unsure about PREFETCH* and CLDEMOTE - both are cache management
insns too, but the emulator currently treats them as a NOP without
invoking any hooks.
I was also uncertain about the new cache_flush_permitted() instance -
generally I think it wouldn't be too bad if we allowed line flushes in
all cases, in which case the checks in the ->wbinvd_intercept() handlers
would suffice (as they did until now).

--- a/tools/fuzz/x86_instruction_emulator/fuzz-emul.c
+++ b/tools/fuzz/x86_instruction_emulator/fuzz-emul.c
@@ -382,10 +382,13 @@ static int fuzz_invlpg(
      return maybe_fail(ctxt, "invlpg", false);
  }
  
-static int fuzz_wbinvd(
+static int fuzz_cache_op(
+    enum x86emul_cache_op op,
+    enum x86_segment seg,
+    unsigned long offset,
      struct x86_emulate_ctxt *ctxt)
  {
-    return maybe_fail(ctxt, "wbinvd", true);
+    return maybe_fail(ctxt, "cache-management", true);
  }
  
  static int fuzz_write_io(
@@ -620,7 +623,7 @@ static const struct x86_emulate_ops all_
      SET(read_xcr),
      SET(read_msr),
      SET(write_msr),
-    SET(wbinvd),
+    SET(cache_op),
      SET(invlpg),
      .get_fpu    = emul_test_get_fpu,
      .put_fpu    = emul_test_put_fpu,
@@ -729,7 +732,7 @@ enum {
      HOOK_read_xcr,
      HOOK_read_msr,
      HOOK_write_msr,
-    HOOK_wbinvd,
+    HOOK_cache_op,
      HOOK_cpuid,
      HOOK_inject_hw_exception,
      HOOK_inject_sw_interrupt,
@@ -773,7 +776,7 @@ static void disable_hooks(struct x86_emu
      MAYBE_DISABLE_HOOK(read_xcr);
      MAYBE_DISABLE_HOOK(read_msr);
      MAYBE_DISABLE_HOOK(write_msr);
-    MAYBE_DISABLE_HOOK(wbinvd);
+    MAYBE_DISABLE_HOOK(cache_op);
      MAYBE_DISABLE_HOOK(cpuid);
      MAYBE_DISABLE_HOOK(get_fpu);
      MAYBE_DISABLE_HOOK(invlpg);
--- a/xen/arch/x86/Rules.mk
+++ b/xen/arch/x86/Rules.mk
@@ -19,7 +19,9 @@ $(call as-option-add,CFLAGS,CC,"crc32 %e
  $(call as-option-add,CFLAGS,CC,"invept (%rax)$$(comma)%rax",-DHAVE_AS_EPT)
  $(call as-option-add,CFLAGS,CC,"rdrand %eax",-DHAVE_AS_RDRAND)
  $(call as-option-add,CFLAGS,CC,"rdfsbase %rax",-DHAVE_AS_FSGSBASE)
+$(call as-option-add,CFLAGS,CC,"xsaveopt (%rax)",-DHAVE_AS_XSAVEOPT)
  $(call as-option-add,CFLAGS,CC,"rdseed %eax",-DHAVE_AS_RDSEED)
+$(call as-option-add,CFLAGS,CC,"clwb (%rax)",-DHAVE_AS_CLWB)
  $(call as-option-add,CFLAGS,CC,".equ \"x\"$$(comma)1", \
                       -U__OBJECT_LABEL__ -DHAVE_AS_QUOTED_SYM \
                       '-D__OBJECT_LABEL__=$(subst $(BASEDIR)/,,$(CURDIR))/$$@')
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -25,6 +25,7 @@
  #include <asm/hvm/trace.h>
  #include <asm/hvm/support.h>
  #include <asm/hvm/svm/svm.h>
+#include <asm/iocap.h>
  #include <asm/vm_event.h>
  
  static void hvmtrace_io_assist(const ioreq_t *p)
@@ -555,16 +556,12 @@ static void *hvmemul_map_linear_addr(
      mfn_t *mfn = &hvmemul_ctxt->mfn[0];
  
      /*
-     * The caller has no legitimate reason for trying a zero-byte write, but
-     * all other code here is written to work if the check below was dropped.
-     *
-     * The maximum write size depends on the number of adjacent mfns[] which
+     * The maximum access size depends on the number of adjacent mfns[] which
       * can be vmap()'d, accouting for possible misalignment within the region.
       * The higher level emulation callers are responsible for ensuring that
-     * mfns[] is large enough for the requested write size.
+     * mfns[] is large enough for the requested access size.
       */
-    if ( bytes == 0 ||
-         nr_frames > ARRAY_SIZE(hvmemul_ctxt->mfn) )
+    if ( nr_frames > ARRAY_SIZE(hvmemul_ctxt->mfn) )
      {
          ASSERT_UNREACHABLE();
          goto unhandleable;
@@ -669,8 +666,6 @@ static void hvmemul_unmap_linear_addr(
      unsigned int i;
      mfn_t *mfn = &hvmemul_ctxt->mfn[0];
  
-    ASSERT(bytes > 0);
-
      if ( nr_frames == 1 )
          unmap_domain_page(mapping);
      else
@@ -1473,7 +1468,10 @@ static int hvmemul_write_msr_discard(
      return X86EMUL_OKAY;
  }
  
-static int hvmemul_wbinvd_discard(
+static int hvmemul_cache_op_discard(
+    enum x86emul_cache_op op,
+    enum x86_segment seg,
+    unsigned long offset,
      struct x86_emulate_ctxt *ctxt)
  {
      return X86EMUL_OKAY;
@@ -2149,10 +2147,65 @@ static int hvmemul_write_msr(
      return rc;
  }
  
-static int hvmemul_wbinvd(
+static int hvmemul_cache_op(
+    enum x86emul_cache_op op,
+    enum x86_segment seg,
+    unsigned long offset,
      struct x86_emulate_ctxt *ctxt)
  {
-    alternative_vcall(hvm_funcs.wbinvd_intercept);
+    struct hvm_emulate_ctxt *hvmemul_ctxt =
+        container_of(ctxt, struct hvm_emulate_ctxt, ctxt);
+    unsigned long addr, reps = 1;
+    uint32_t pfec = PFEC_page_present;
+    int rc;
+    void *mapping;
+
+    if ( !cache_flush_permitted(current->domain) )
+        return X86EMUL_OKAY;
+
+    switch ( op )
+    {
+    case x86emul_clflush:
+    case x86emul_clflushopt:
+    case x86emul_clwb:
+        ASSERT(!is_x86_system_segment(seg));
+
+        rc = hvmemul_virtual_to_linear(seg, offset, 0, &reps,
+                                       hvm_access_read, hvmemul_ctxt, &addr);
+        if ( rc != X86EMUL_OKAY )
+            break;
+
+        if ( hvmemul_ctxt->seg_reg[x86_seg_ss].dpl == 3 )
+            pfec |= PFEC_user_mode;
+
+        mapping = hvmemul_map_linear_addr(addr, 0, pfec, hvmemul_ctxt,
+                                          current->arch.hvm.data_cache);
+        if ( mapping == ERR_PTR(~X86EMUL_EXCEPTION) )
+            return X86EMUL_EXCEPTION;
+        if ( IS_ERR_OR_NULL(mapping) )
+            break;
+
+        if ( cpu_has_clflush )
+        {
+            if ( op == x86emul_clwb && cpu_has_clwb )
+                clwb(mapping);
+            else if ( op == x86emul_clflushopt && cpu_has_clflushopt )
+                clflushopt(mapping);
+            else
+                clflush(mapping);
+
+            hvmemul_unmap_linear_addr(mapping, addr, 0, hvmemul_ctxt);
+            break;
+        }
+
+        hvmemul_unmap_linear_addr(mapping, addr, 0, hvmemul_ctxt);
+        /* fall through */
+    case x86emul_invd:
+    case x86emul_wbinvd:
+        alternative_vcall(hvm_funcs.wbinvd_intercept);
+        break;
+    }
+
      return X86EMUL_OKAY;
  }
  
@@ -2353,7 +2406,7 @@ static const struct x86_emulate_ops hvm_
      .write_xcr     = hvmemul_write_xcr,
      .read_msr      = hvmemul_read_msr,
      .write_msr     = hvmemul_write_msr,
-    .wbinvd        = hvmemul_wbinvd,
+    .cache_op      = hvmemul_cache_op,
      .cpuid         = x86emul_cpuid,
      .get_fpu       = hvmemul_get_fpu,
      .put_fpu       = hvmemul_put_fpu,
@@ -2380,7 +2433,7 @@ static const struct x86_emulate_ops hvm_
      .write_xcr     = hvmemul_write_xcr,
      .read_msr      = hvmemul_read_msr,
      .write_msr     = hvmemul_write_msr_discard,
-    .wbinvd        = hvmemul_wbinvd_discard,
+    .cache_op      = hvmemul_cache_op_discard,
      .cpuid         = x86emul_cpuid,
      .get_fpu       = hvmemul_get_fpu,
      .put_fpu       = hvmemul_put_fpu,
--- a/xen/arch/x86/pv/emul-priv-op.c
+++ b/xen/arch/x86/pv/emul-priv-op.c
@@ -1118,9 +1118,11 @@ static int write_msr(unsigned int reg, u
      return X86EMUL_UNHANDLEABLE;
  }
  
-/* Name it differently to avoid clashing with wbinvd() */
-static int _wbinvd(struct x86_emulate_ctxt *ctxt)
+static int cache_op(enum x86emul_cache_op op, enum x86_segment seg,
+                    unsigned long offset, struct x86_emulate_ctxt *ctxt)
  {
+    ASSERT(op == x86emul_wbinvd);
+
      /* Ignore the instruction if unprivileged. */
      if ( !cache_flush_permitted(current->domain) )
          /*
@@ -1238,7 +1240,7 @@ static const struct x86_emulate_ops priv
      .read_msr            = read_msr,
      .write_msr           = write_msr,
      .cpuid               = x86emul_cpuid,
-    .wbinvd              = _wbinvd,
+    .cache_op            = cache_op,
  };
  
  int pv_emulate_privileged_op(struct cpu_user_regs *regs)
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -5933,8 +5933,11 @@ x86_emulate(
      case X86EMUL_OPC(0x0f, 0x08): /* invd */
      case X86EMUL_OPC(0x0f, 0x09): /* wbinvd */
          generate_exception_if(!mode_ring0(), EXC_GP, 0);
-        fail_if(ops->wbinvd == NULL);
-        if ( (rc = ops->wbinvd(ctxt)) != 0 )
+        fail_if(!ops->cache_op);
+        if ( (rc = ops->cache_op(b == 0x09 ? x86emul_wbinvd
+                                           : x86emul_invd,
+                                 x86_seg_none, 0,
+                                 ctxt)) != X86EMUL_OKAY )
              goto done;
          break;
  
@@ -7801,8 +7804,9 @@ x86_emulate(
              /* else clwb */
              fail_if(!vex.pfx);
              vcpu_must_have(clwb);
-            fail_if(!ops->wbinvd);
-            if ( (rc = ops->wbinvd(ctxt)) != X86EMUL_OKAY )
+            fail_if(!ops->cache_op);
+            if ( (rc = ops->cache_op(x86emul_clwb, ea.mem.seg, ea.mem.off,
+                                     ctxt)) != X86EMUL_OKAY )
                  goto done;
              break;
          case 7:
@@ -7818,8 +7822,11 @@ x86_emulate(
                  vcpu_must_have(clflush);
              else
                  vcpu_must_have(clflushopt);
-            fail_if(ops->wbinvd == NULL);
-            if ( (rc = ops->wbinvd(ctxt)) != 0 )
+            fail_if(!ops->cache_op);
+            if ( (rc = ops->cache_op(vex.pfx ? x86emul_clflushopt
+                                             : x86emul_clflush,
+                                     ea.mem.seg, ea.mem.off,
+                                     ctxt)) != X86EMUL_OKAY )
                  goto done;
              break;
          default:
--- a/xen/arch/x86/x86_emulate/x86_emulate.h
+++ b/xen/arch/x86/x86_emulate/x86_emulate.h
@@ -176,6 +176,14 @@ enum x86_emulate_fpu_type {
      X86EMUL_FPU_none
  };
  
+enum x86emul_cache_op {
+    x86emul_clflush,
+    x86emul_clflushopt,
+    x86emul_clwb,
+    x86emul_invd,
+    x86emul_wbinvd,
+};
+
  struct x86_emulate_state;
  
  /*
@@ -452,8 +460,15 @@ struct x86_emulate_ops
          uint64_t val,
          struct x86_emulate_ctxt *ctxt);
  
-    /* wbinvd: Write-back and invalidate cache contents. */
-    int (*wbinvd)(
+    /*
+     * cache_op: Write-back and/or invalidate cache contents.
+     *
+     * @seg:@offset applicable only to some of enum x86emul_cache_op.
+     */
+    int (*cache_op)(
+        enum x86emul_cache_op op,
+        enum x86_segment seg,
+        unsigned long offset,
          struct x86_emulate_ctxt *ctxt);
  
      /* cpuid: Emulate CPUID via given set of EAX-EDX inputs/outputs. */
--- a/xen/include/asm-x86/cpufeature.h
+++ b/xen/include/asm-x86/cpufeature.h
@@ -102,6 +102,8 @@
  #define cpu_has_rdseed          boot_cpu_has(X86_FEATURE_RDSEED)
  #define cpu_has_smap            boot_cpu_has(X86_FEATURE_SMAP)
  #define cpu_has_avx512_ifma     boot_cpu_has(X86_FEATURE_AVX512_IFMA)
+#define cpu_has_clflushopt      boot_cpu_has(X86_FEATURE_CLFLUSHOPT)
+#define cpu_has_clwb            boot_cpu_has(X86_FEATURE_CLWB)
  #define cpu_has_avx512er        boot_cpu_has(X86_FEATURE_AVX512ER)
  #define cpu_has_avx512cd        boot_cpu_has(X86_FEATURE_AVX512CD)
  #define cpu_has_sha             boot_cpu_has(X86_FEATURE_SHA)
--- a/xen/include/asm-x86/system.h
+++ b/xen/include/asm-x86/system.h
@@ -21,6 +21,23 @@ static inline void clflush(const void *p
      asm volatile ( "clflush %0" :: "m" (*(const char *)p) );
  }
  
+static inline void clflushopt(const void *p)
+{
+    asm volatile ( "data16 clflush %0" :: "m" (*(const char *)p) );
+}
+
+static inline void clwb(const void *p)
+{
+#if defined(HAVE_AS_CLWB)
+    asm volatile ( "clwb %0" :: "m" (*(const char *)p) );
+#elif defined(HAVE_AS_XSAVEOPT)
+    asm volatile ( "data16 xsaveopt %0" :: "m" (*(const char *)p) );
+#else
+    asm volatile ( ".byte 0x66, 0x0f, 0xae, 0x32"
+                   :: "d" (p), "m" (*(const char *)p) );
+#endif
+}
+
  #define xchg(ptr,v) \
      ((__typeof__(*(ptr)))__xchg((unsigned long)(v),(ptr),sizeof(*(ptr))))
  

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