--- a/tools/tests/x86_emulator/Makefile
+++ b/tools/tests/x86_emulator/Makefile
@@ -18,7 +18,7 @@ CFLAGS += $(CFLAGS_xeninclude)
 
 SIMD := 3dnow sse sse2 sse4 avx avx2 xop avx512f avx512bw avx512dq avx512er
 FMA := fma4 fma
-SG := avx2-sg
+SG := avx2-sg avx512f-sg avx512vl-sg
 TESTCASES := blowfish $(SIMD) $(FMA) $(SG)
 
 OPMASK := avx512f avx512dq avx512bw
@@ -66,6 +66,14 @@ xop-flts := $(avx-flts)
 avx512f-vecs := 64 16 32
 avx512f-ints := 4 8
 avx512f-flts := 4 8
+avx512f-sg-vecs := 64
+avx512f-sg-idxs := 4 8
+avx512f-sg-ints := $(avx512f-ints)
+avx512f-sg-flts := $(avx512f-flts)
+avx512vl-sg-vecs := 16 32
+avx512vl-sg-idxs := $(avx512f-sg-idxs)
+avx512vl-sg-ints := $(avx512f-ints)
+avx512vl-sg-flts := $(avx512f-flts)
 avx512bw-vecs := $(avx512f-vecs)
 avx512bw-ints := 1 2
 avx512bw-flts :=
--- a/tools/tests/x86_emulator/evex-disp8.c
+++ b/tools/tests/x86_emulator/evex-disp8.c
@@ -176,6 +176,8 @@ static const struct test avx512f_all[] =
     INSN(fnmsub213,    66, 0f38, af,    el,     sd, el),
     INSN(fnmsub231,    66, 0f38, be,    vl,     sd, vl),
     INSN(fnmsub231,    66, 0f38, bf,    el,     sd, el),
+    INSN(gatherd,      66, 0f38, 92,    vl,     sd, el),
+    INSN(gatherq,      66, 0f38, 93,    vl,     sd, el),
     INSN(getexp,       66, 0f38, 42,    vl,     sd, vl),
     INSN(getexp,       66, 0f38, 43,    el,     sd, el),
     INSN(getmant,      66, 0f3a, 26,    vl,     sd, vl),
@@ -229,6 +231,8 @@ static const struct test avx512f_all[] =
     INSN(permt2,       66, 0f38, 7e,    vl,     dq, vl),
     INSN(permt2,       66, 0f38, 7f,    vl,     sd, vl),
     INSN(pexpand,      66, 0f38, 89,    vl,     dq, el),
+    INSN(pgatherd,     66, 0f38, 90,    vl,     dq, el),
+    INSN(pgatherq,     66, 0f38, 91,    vl,     dq, el),
     INSN(pmaxs,        66, 0f38, 3d,    vl,     dq, vl),
     INSN(pmaxu,        66, 0f38, 3f,    vl,     dq, vl),
     INSN(pmins,        66, 0f38, 39,    vl,     dq, vl),
@@ -698,7 +702,7 @@ static void test_one(const struct test *
     instr[3] = evex.raw[2];
     instr[4] = test->opc;
     instr[5] = 0x44 | (test->ext << 3); /* ModR/M */
-    instr[6] = 0x12; /* SIB: base rDX, index none / xMM4 */
+    instr[6] = 0x22; /* SIB: base rDX, index none / xMM4 */
     instr[7] = 1; /* Disp8 */
     instr[8] = 0; /* immediate, if any */
 
@@ -718,7 +722,8 @@ static void test_one(const struct test *
          if ( accessed[i] )
              goto fail;
     for ( ; i < (test->scale == SC_vl ? vsz : esz) + (sg ? esz : vsz); ++i )
-         if ( accessed[i] != (sg ? vsz / esz : 1) )
+         if ( accessed[i] != (sg ? (vsz / esz) >> (test->opc & 1 & !evex.w)
+                                 : 1) )
              goto fail;
     for ( ; i < ARRAY_SIZE(accessed); ++i )
          if ( accessed[i] )
--- a/tools/tests/x86_emulator/simd-sg.c
+++ b/tools/tests/x86_emulator/simd-sg.c
@@ -35,13 +35,78 @@ typedef long long __attribute__((vector_
 #define ITEM_COUNT (VEC_SIZE / ELEM_SIZE < IVEC_SIZE / IDX_SIZE ? \
                     VEC_SIZE / ELEM_SIZE : IVEC_SIZE / IDX_SIZE)
 
-#if VEC_SIZE == 16
-# define to_bool(cmp) __builtin_ia32_ptestc128(cmp, (vec_t){} == 0)
-#else
-# define to_bool(cmp) __builtin_ia32_ptestc256(cmp, (vec_t){} == 0)
-#endif
+#if defined(__AVX512F__)
+# define ALL_TRUE (~0ULL >> (64 - ELEM_COUNT))
+# if ELEM_SIZE == 4
+#  if IDX_SIZE == 4 || defined(__AVX512VL__)
+#   define to_mask(msk) B(ptestmd, , (vsi_t)(msk), (vsi_t)(msk), ~0)
+#   define eq(x, y) (B(pcmpeqd, _mask, (vsi_t)(x), (vsi_t)(y), -1) == ALL_TRUE)
+#  else
+#   define widen(x) __builtin_ia32_pmovzxdq512_mask((vsi_t)(x), (idi_t){}, ~0)
+#   define to_mask(msk) __builtin_ia32_ptestmq512(widen(msk), widen(msk), ~0)
+#   define eq(x, y) (__builtin_ia32_pcmpeqq512_mask(widen(x), widen(y), ~0) == ALL_TRUE)
+#  endif
+#  define BG_(dt, it, reg, mem, idx, msk, scl) \
+    __builtin_ia32_gather##it##dt(reg, mem, idx, to_mask(msk), scl)
+# else
+#  define eq(x, y) (B(pcmpeqq, _mask, (vdi_t)(x), (vdi_t)(y), -1) == ALL_TRUE)
+#  define BG_(dt, it, reg, mem, idx, msk, scl) \
+    __builtin_ia32_gather##it##dt(reg, mem, idx, B(ptestmq, , (vdi_t)(msk), (vdi_t)(msk), ~0), scl)
+# endif
+/*
+ * Instead of replicating the main IDX_SIZE conditional below three times, use
+ * a double layer of macro invocations, allowing for substitution of the
+ * respective relevant macro argument tokens.
+ */
+# define BG(dt, it, reg, mem, idx, msk, scl) BG_(dt, it, reg, mem, idx, msk, scl)
+# if VEC_MAX < 64
+/*
+ * The sub-512-bit built-ins have an extra "3" infix, presumably because the
+ * 512-bit names were chosen without the AVX512VL extension in mind (and hence
+ * making the latter collide with the AVX2 ones).
+ */
+#  define si 3si
+#  define di 3di
+# endif
+# if VEC_MAX == 16
+#  define v8df v2df
+#  define v8di v2di
+#  define v16sf v4sf
+#  define v16si v4si
+# elif VEC_MAX == 32
+#  define v8df v4df
+#  define v8di v4di
+#  define v16sf v8sf
+#  define v16si v8si
+# endif
+# if IDX_SIZE == 4
+#  if INT_SIZE == 4
+#   define gather(reg, mem, idx, msk, scl) BG(v16si, si, reg, mem, idx, msk, scl)
+#  elif INT_SIZE == 8
+#   define gather(reg, mem, idx, msk, scl) (vec_t)(BG(v8di, si, (vdi_t)(reg), mem, idx, msk, scl))
+#  elif FLOAT_SIZE == 4
+#   define gather(reg, mem, idx, msk, scl) BG(v16sf, si, reg, mem, idx, msk, scl)
+#  elif FLOAT_SIZE == 8
+#   define gather(reg, mem, idx, msk, scl) BG(v8df, si, reg, mem, idx, msk, scl)
+#  endif
+# elif IDX_SIZE == 8
+#  if INT_SIZE == 4
+#   define gather(reg, mem, idx, msk, scl) BG(v16si, di, reg, mem, (idi_t)(idx), msk, scl)
+#  elif INT_SIZE == 8
+#   define gather(reg, mem, idx, msk, scl) (vec_t)(BG(v8di, di, (vdi_t)(reg), mem, (idi_t)(idx), msk, scl))
+#  elif FLOAT_SIZE == 4
+#   define gather(reg, mem, idx, msk, scl) BG(v16sf, di, reg, mem, (idi_t)(idx), msk, scl)
+#  elif FLOAT_SIZE == 8
+#   define gather(reg, mem, idx, msk, scl) BG(v8df, di, reg, mem, (idi_t)(idx), msk, scl)
+#  endif
+# endif
+#elif defined(__AVX2__)
+# if VEC_SIZE == 16
+#  define to_bool(cmp) __builtin_ia32_ptestc128(cmp, (vec_t){} == 0)
+# else
+#  define to_bool(cmp) __builtin_ia32_ptestc256(cmp, (vec_t){} == 0)
+# endif
 
-#if defined(__AVX2__)
 # if VEC_MAX == 16
 #  if IDX_SIZE == 4
 #   if INT_SIZE == 4
@@ -111,6 +176,10 @@ typedef long long __attribute__((vector_
 # endif
 #endif
 
+#ifndef eq
+# define eq(x, y) to_bool((x) == (y))
+#endif
+
 #define GLUE_(x, y) x ## y
 #define GLUE(x, y) GLUE_(x, y)
 
@@ -119,6 +188,7 @@ typedef long long __attribute__((vector_
 #define PUT8(n)  PUT4(n),   PUT4((n) +  4)
 #define PUT16(n) PUT8(n),   PUT8((n) +  8)
 #define PUT32(n) PUT16(n), PUT16((n) + 16)
+#define PUT64(n) PUT32(n), PUT32((n) + 32)
 
 const typeof((vec_t){}[0]) array[] = {
     GLUE(PUT, VEC_MAX)(1),
@@ -174,7 +244,7 @@ int sg_test(void)
 
     y = gather(full, array + ITEM_COUNT, -idx, full, ELEM_SIZE);
 #if ITEM_COUNT == ELEM_COUNT
-    if ( !to_bool(y == x - 1) )
+    if ( !eq(y, x - 1) )
         return __LINE__;
 #else
     for ( i = 0; i < ITEM_COUNT; ++i )
--- a/tools/tests/x86_emulator/test_x86_emulator.c
+++ b/tools/tests/x86_emulator/test_x86_emulator.c
@@ -22,6 +22,8 @@ asm ( ".pushsection .test, \"ax\", @prog
 #include "avx512dq-opmask.h"
 #include "avx512bw-opmask.h"
 #include "avx512f.h"
+#include "avx512f-sg.h"
+#include "avx512vl-sg.h"
 #include "avx512bw.h"
 #include "avx512dq.h"
 #include "avx512er.h"
@@ -90,11 +92,13 @@ static bool simd_check_avx512f(void)
     return cpu_has_avx512f;
 }
 #define simd_check_avx512f_opmask simd_check_avx512f
+#define simd_check_avx512f_sg simd_check_avx512f
 
 static bool simd_check_avx512f_vl(void)
 {
     return cpu_has_avx512f && cpu_has_avx512vl;
 }
+#define simd_check_avx512vl_sg simd_check_avx512f_vl
 
 static bool simd_check_avx512dq(void)
 {
@@ -291,6 +295,14 @@ static const struct {
     SIMD(AVX512F u32x16,      avx512f,      64u4),
     SIMD(AVX512F s64x8,       avx512f,      64i8),
     SIMD(AVX512F u64x8,       avx512f,      64u8),
+    SIMD(AVX512F S/G f32[16x32], avx512f_sg, 64x4f4),
+    SIMD(AVX512F S/G f64[ 8x32], avx512f_sg, 64x4f8),
+    SIMD(AVX512F S/G f32[ 8x64], avx512f_sg, 64x8f4),
+    SIMD(AVX512F S/G f64[ 8x64], avx512f_sg, 64x8f8),
+    SIMD(AVX512F S/G i32[16x32], avx512f_sg, 64x4i4),
+    SIMD(AVX512F S/G i64[ 8x32], avx512f_sg, 64x4i8),
+    SIMD(AVX512F S/G i32[ 8x64], avx512f_sg, 64x8i4),
+    SIMD(AVX512F S/G i64[ 8x64], avx512f_sg, 64x8i8),
     AVX512VL(VL f32x4,        avx512f,      16f4),
     AVX512VL(VL f64x2,        avx512f,      16f8),
     AVX512VL(VL f32x8,        avx512f,      32f4),
@@ -303,6 +315,22 @@ static const struct {
     AVX512VL(VL u64x2,        avx512f,      16u8),
     AVX512VL(VL s64x4,        avx512f,      32i8),
     AVX512VL(VL u64x4,        avx512f,      32u8),
+    SIMD(AVX512VL S/G f32[4x32], avx512vl_sg, 16x4f4),
+    SIMD(AVX512VL S/G f64[2x32], avx512vl_sg, 16x4f8),
+    SIMD(AVX512VL S/G f32[2x64], avx512vl_sg, 16x8f4),
+    SIMD(AVX512VL S/G f64[2x64], avx512vl_sg, 16x8f8),
+    SIMD(AVX512VL S/G f32[8x32], avx512vl_sg, 32x4f4),
+    SIMD(AVX512VL S/G f64[4x32], avx512vl_sg, 32x4f8),
+    SIMD(AVX512VL S/G f32[4x64], avx512vl_sg, 32x8f4),
+    SIMD(AVX512VL S/G f64[4x64], avx512vl_sg, 32x8f8),
+    SIMD(AVX512VL S/G i32[4x32], avx512vl_sg, 16x4i4),
+    SIMD(AVX512VL S/G i64[2x32], avx512vl_sg, 16x4i8),
+    SIMD(AVX512VL S/G i32[2x64], avx512vl_sg, 16x8i4),
+    SIMD(AVX512VL S/G i64[2x64], avx512vl_sg, 16x8i8),
+    SIMD(AVX512VL S/G i32[8x32], avx512vl_sg, 32x4i4),
+    SIMD(AVX512VL S/G i64[4x32], avx512vl_sg, 32x4i8),
+    SIMD(AVX512VL S/G i32[4x64], avx512vl_sg, 32x8i4),
+    SIMD(AVX512VL S/G i64[4x64], avx512vl_sg, 32x8i8),
     SIMD(AVX512BW s8x64,     avx512bw,      64i1),
     SIMD(AVX512BW u8x64,     avx512bw,      64u1),
     SIMD(AVX512BW s16x32,    avx512bw,      64i2),
@@ -4260,7 +4288,7 @@ int main(int argc, char **argv)
 
         if ( !blobs[j].size )
         {
-            printf("%-39s n/a\n", blobs[j].name);
+            printf("%-39s n/a (%u-bit)\n", blobs[j].name, blobs[j].bitness);
             continue;
         }
 
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -499,7 +499,7 @@ static const struct ext0f38_table {
     [0x8c] = { .simd_size = simd_packed_int },
     [0x8d] = { .simd_size = simd_packed_int, .d8s = d8s_vl },
     [0x8e] = { .simd_size = simd_packed_int, .to_mem = 1 },
-    [0x90 ... 0x93] = { .simd_size = simd_other, .vsib = 1 },
+    [0x90 ... 0x93] = { .simd_size = simd_other, .vsib = 1, .d8s = d8s_dq },
     [0x96 ... 0x98] = { .simd_size = simd_packed_fp, .d8s = d8s_vl },
     [0x99] = { .simd_size = simd_scalar_vexw, .d8s = d8s_dq },
     [0x9a] = { .simd_size = simd_packed_fp, .d8s = d8s_vl },
@@ -3054,7 +3054,8 @@ x86_decode(
 
         d &= ~ModRM;
 #undef ModRM /* Only its aliases are valid to use from here on. */
-        modrm_reg = ((rex_prefix & 4) << 1) | ((modrm & 0x38) >> 3);
+        modrm_reg = ((rex_prefix & 4) << 1) | ((modrm & 0x38) >> 3) |
+                    ((evex_encoded() && !evex.R) << 4);
         modrm_rm  = modrm & 0x07;
 
         /*
@@ -3224,7 +3225,8 @@ x86_decode(
         if ( modrm_mod == 3 )
         {
             generate_exception_if(d & vSIB, EXC_UD);
-            modrm_rm |= (rex_prefix & 1) << 3;
+            modrm_rm |= ((rex_prefix & 1) << 3) |
+                        (evex_encoded() && !evex.x) << 4;
             ea.type = OP_REG;
         }
         else if ( ad_bytes == 2 )
@@ -3289,7 +3291,10 @@ x86_decode(
 
                 state->sib_index = ((sib >> 3) & 7) | ((rex_prefix << 2) & 8);
                 state->sib_scale = (sib >> 6) & 3;
-                if ( state->sib_index != 4 && !(d & vSIB) )
+                if ( unlikely(d & vSIB) )
+                    state->sib_index |= (mode_64bit() && evex_encoded() &&
+                                         !evex.RX) << 4;
+                else if ( state->sib_index != 4 )
                 {
                     ea.mem.off = *decode_gpr(state->regs, state->sib_index);
                     ea.mem.off <<= state->sib_scale;
@@ -3592,7 +3597,7 @@ x86_emulate(
     generate_exception_if(state->not_64bit && mode_64bit(), EXC_UD);
 
     if ( ea.type == OP_REG )
-        ea.reg = _decode_gpr(&_regs, modrm_rm, (d & ByteOp) && !rex_prefix);
+        ea.reg = _decode_gpr(&_regs, modrm_rm, (d & ByteOp) && !rex_prefix && !vex.opcx);
 
     memset(mmvalp, 0xaa /* arbitrary */, sizeof(*mmvalp));
 
@@ -3606,7 +3611,7 @@ x86_emulate(
         src.type = OP_REG;
         if ( d & ByteOp )
         {
-            src.reg = _decode_gpr(&_regs, modrm_reg, !rex_prefix);
+            src.reg = _decode_gpr(&_regs, modrm_reg, !rex_prefix && !vex.opcx);
             src.val = *(uint8_t *)src.reg;
             src.bytes = 1;
         }
@@ -3704,7 +3709,7 @@ x86_emulate(
         dst.type = OP_REG;
         if ( d & ByteOp )
         {
-            dst.reg = _decode_gpr(&_regs, modrm_reg, !rex_prefix);
+            dst.reg = _decode_gpr(&_regs, modrm_reg, !rex_prefix && !vex.opcx);
             dst.val = *(uint8_t *)dst.reg;
             dst.bytes = 1;
         }
@@ -9119,6 +9124,130 @@ x86_emulate(
         put_stub(stub);
 
         state->simd_size = simd_none;
+        break;
+    }
+
+    case X86EMUL_OPC_EVEX_66(0x0f38, 0x90): /* vpgatherd{d,q} mem,[xyz]mm{k} */
+    case X86EMUL_OPC_EVEX_66(0x0f38, 0x91): /* vpgatherq{d,q} mem,[xyz]mm{k} */
+    case X86EMUL_OPC_EVEX_66(0x0f38, 0x92): /* vgatherdp{s,d} mem,[xyz]mm{k} */
+    case X86EMUL_OPC_EVEX_66(0x0f38, 0x93): /* vgatherqp{s,d} mem,[xyz]mm{k} */
+    {
+        typeof(evex) *pevex;
+        union {
+            int32_t dw[16];
+            int64_t qw[8];
+        } index;
+        bool done = false;
+
+        ASSERT(ea.type == OP_MEM);
+        generate_exception_if((!evex.opmsk || evex.brs || evex.z ||
+                               evex.reg != 0xf ||
+                               modrm_reg == state->sib_index),
+                              EXC_UD);
+        avx512_vlen_check(false);
+        host_and_vcpu_must_have(avx512f);
+        get_fpu(X86EMUL_FPU_zmm);
+
+        /* Read destination and index registers. */
+        opc = init_evex(stub);
+        pevex = copy_EVEX(opc, evex);
+        pevex->opcx = vex_0f;
+        opc[0] = 0x7f; /* vmovdqa{32,64} */
+        /*
+         * The register writeback below has to retain masked-off elements, but
+         * needs to clear upper portions in the index-wider-than-data cases.
+         * Therefore read (and write below) the full register. The alternative
+         * would have been to fiddle with the mask register used.
+         */
+        pevex->opmsk = 0;
+        /* Use (%rax) as destination and modrm_reg as source. */
+        pevex->b = 1;
+        opc[1] = (modrm_reg & 7) << 3;
+        pevex->RX = 1;
+        opc[2] = 0xc3;
+
+        invoke_stub("", "", "=m" (*mmvalp) : "a" (mmvalp));
+
+        pevex->pfx = vex_f3; /* vmovdqu{32,64} */
+        pevex->w = b & 1;
+        /* Switch to sib_index as source. */
+        pevex->r = !mode_64bit() || !(state->sib_index & 0x08);
+        pevex->R = !mode_64bit() || !(state->sib_index & 0x10);
+        opc[1] = (state->sib_index & 7) << 3;
+
+        invoke_stub("", "", "=m" (index) : "a" (&index));
+        put_stub(stub);
+
+        /* Clear untouched parts of the destination and mask values. */
+        n = 1 << (2 + evex.lr - ((b & 1) | evex.w));
+        op_bytes = 4 << evex.w;
+        memset((void *)mmvalp + n * op_bytes, 0, 64 - n * op_bytes);
+        op_mask &= (1 << n) - 1;
+
+        for ( i = 0; op_mask; ++i )
+        {
+            signed long idx = b & 1 ? index.qw[i] : index.dw[i];
+
+            if ( !(op_mask & (1 << i)) )
+                continue;
+
+            rc = ops->read(ea.mem.seg,
+                           truncate_ea(ea.mem.off + (idx << state->sib_scale)),
+                           (void *)mmvalp + i * op_bytes, op_bytes, ctxt);
+            if ( rc != X86EMUL_OKAY )
+            {
+                /*
+                 * If we've made some progress and the access did not fault,
+                 * force a retry instead. This is for example necessary to
+                 * cope with the limited capacity of HVM's MMIO cache.
+                 */
+                if ( rc != X86EMUL_EXCEPTION && done )
+                    rc = X86EMUL_RETRY;
+                break;
+            }
+
+            op_mask &= ~(1 << i);
+            done = true;
+
+#ifdef __XEN__
+            if ( op_mask && local_events_need_delivery() )
+            {
+                rc = X86EMUL_RETRY;
+                break;
+            }
+#endif
+        }
+
+        /* Write destination and mask registers. */
+        opc = init_evex(stub);
+        pevex = copy_EVEX(opc, evex);
+        pevex->opcx = vex_0f;
+        opc[0] = 0x6f; /* vmovdqa{32,64} */
+        pevex->opmsk = 0;
+        /* Use modrm_reg as destination and (%rax) as source. */
+        pevex->b = 1;
+        opc[1] = (modrm_reg & 7) << 3;
+        pevex->RX = 1;
+        opc[2] = 0xc3;
+
+        invoke_stub("", "", "+m" (*mmvalp) : "a" (mmvalp));
+
+        /*
+         * kmovw: This is VEX-encoded, so we can't use pevex. Avoid copy_VEX() etc
+         * as well, since we can easily use the 2-byte VEX form here.
+         */
+        opc -= EVEX_PFX_BYTES;
+        opc[0] = 0xc5;
+        opc[1] = 0xf8;
+        opc[2] = 0x90;
+        /* Use (%rax) as source. */
+        opc[3] = evex.opmsk << 3;
+        opc[4] = 0xc3;
+
+        invoke_stub("", "", "+m" (op_mask) : "a" (&op_mask));
+        put_stub(stub);
+
+        state->simd_size = simd_none;
         break;
     }
 
--- a/xen/arch/x86/x86_emulate/x86_emulate.h
+++ b/xen/arch/x86/x86_emulate/x86_emulate.h
@@ -662,8 +662,6 @@ static inline unsigned long *decode_gpr(
     BUILD_BUG_ON(ARRAY_SIZE(cpu_user_regs_gpr_offsets) &
                  (ARRAY_SIZE(cpu_user_regs_gpr_offsets) - 1));
 
-    ASSERT(modrm < ARRAY_SIZE(cpu_user_regs_gpr_offsets));
-
     /* Note that this also acts as array_access_nospec() stand-in. */
     modrm &= ARRAY_SIZE(cpu_user_regs_gpr_offsets) - 1;
 
