qemu-kvm/kvm-x86-Grant-AMX-permission-for-guest.patch

From 50840e01d05a466a1dfbc219e49233834e5d7ed0 Mon Sep 17 00:00:00 2001
From: Yang Zhong <yang.zhong@intel.com>
Date: Wed, 16 Feb 2022 22:04:29 -0800
Subject: [PATCH 07/24] x86: Grant AMX permission for guest

RH-Author: Paul Lai <plai@redhat.com>
RH-MergeRequest: 176: Enable KVM AMX support
RH-Commit: [7/13] 437578191f61139ca710cc7045ab38eb0d05eae2
RH-Bugzilla: 1916415
RH-Acked-by: Cornelia Huck <cohuck@redhat.com>
RH-Acked-by: Igor Mammedov <imammedo@redhat.com>
RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Kernel allocates 4K xstate buffer by default. For XSAVE features
which require large state component (e.g. AMX), Linux kernel
dynamically expands the xstate buffer only after the process has
acquired the necessary permissions. Those are called dynamically-
enabled XSAVE features (or dynamic xfeatures).

There are separate permissions for native tasks and guests.

Qemu should request the guest permissions for dynamic xfeatures
which will be exposed to the guest. This only needs to be done
once before the first vcpu is created.

KVM implemented one new ARCH_GET_XCOMP_SUPP system attribute API to
get host side supported_xcr0 and Qemu can decide if it can request
dynamically enabled XSAVE features permission.
https://lore.kernel.org/all/20220126152210.3044876-1-pbonzini@redhat.com/

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Message-Id: <20220217060434.52460-4-yang.zhong@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 19db68ca68a78fa033a21d419036b6e416554564)
Signed-off-by: Paul Lai <plai@redhat.com>
---
 target/i386/cpu.c          |  7 +++++
 target/i386/cpu.h          |  4 +++
 target/i386/kvm/kvm-cpu.c  | 12 ++++----
 target/i386/kvm/kvm.c      | 57 ++++++++++++++++++++++++++++++++++++++
 target/i386/kvm/kvm_i386.h |  1 +
 5 files changed, 75 insertions(+), 6 deletions(-)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 0453c27c9d..c19b51ea32 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -6027,6 +6027,7 @@ static void x86_cpu_enable_xsave_components(X86CPU *cpu)
     CPUX86State *env = &cpu->env;
     int i;
     uint64_t mask;
+    static bool request_perm;
 
     if (!(env->features[FEAT_1_ECX] & CPUID_EXT_XSAVE)) {
         env->features[FEAT_XSAVE_COMP_LO] = 0;
@@ -6042,6 +6043,12 @@ static void x86_cpu_enable_xsave_components(X86CPU *cpu)
         }
     }
 
+    /* Only request permission for first vcpu */
+    if (kvm_enabled() && !request_perm) {
+        kvm_request_xsave_components(cpu, mask);
+        request_perm = true;
+    }
+
     env->features[FEAT_XSAVE_COMP_LO] = mask;
     env->features[FEAT_XSAVE_COMP_HI] = mask >> 32;
 }
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index e1dd8b9555..58676390e6 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -549,6 +549,10 @@ typedef enum X86Seg {
 #define XSTATE_ZMM_Hi256_MASK           (1ULL << XSTATE_ZMM_Hi256_BIT)
 #define XSTATE_Hi16_ZMM_MASK            (1ULL << XSTATE_Hi16_ZMM_BIT)
 #define XSTATE_PKRU_MASK                (1ULL << XSTATE_PKRU_BIT)
+#define XSTATE_XTILE_CFG_MASK           (1ULL << XSTATE_XTILE_CFG_BIT)
+#define XSTATE_XTILE_DATA_MASK          (1ULL << XSTATE_XTILE_DATA_BIT)
+
+#define XSTATE_DYNAMIC_MASK             (XSTATE_XTILE_DATA_MASK)
 
 #define ESA_FEATURE_ALIGN64_BIT         1
 
diff --git a/target/i386/kvm/kvm-cpu.c b/target/i386/kvm/kvm-cpu.c
index 86ef7b2712..bdc967c484 100644
--- a/target/i386/kvm/kvm-cpu.c
+++ b/target/i386/kvm/kvm-cpu.c
@@ -84,7 +84,7 @@ static void kvm_cpu_max_instance_init(X86CPU *cpu)
 static void kvm_cpu_xsave_init(void)
 {
     static bool first = true;
-    KVMState *s = kvm_state;
+    uint32_t eax, ebx, ecx, edx;
     int i;
 
     if (!first) {
@@ -100,11 +100,11 @@ static void kvm_cpu_xsave_init(void)
         ExtSaveArea *esa = &x86_ext_save_areas[i];
 
         if (esa->size) {
-            int sz = kvm_arch_get_supported_cpuid(s, 0xd, i, R_EAX);
-            if (sz != 0) {
-                assert(esa->size == sz);
-                esa->offset = kvm_arch_get_supported_cpuid(s, 0xd, i, R_EBX);
-                esa->ecx = kvm_arch_get_supported_cpuid(s, 0xd, i, R_ECX);
+            host_cpuid(0xd, i, &eax, &ebx, &ecx, &edx);
+            if (eax != 0) {
+                assert(esa->size == eax);
+                esa->offset = ebx;
+                esa->ecx = ecx;
             }
         }
     }
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index a668f521ac..b5d98c4361 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -17,6 +17,7 @@
 #include "qapi/error.h"
 #include <sys/ioctl.h>
 #include <sys/utsname.h>
+#include <sys/syscall.h>
 
 #include <linux/kvm.h>
 #include "standard-headers/asm-x86/kvm_para.h"
@@ -347,6 +348,7 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
     struct kvm_cpuid2 *cpuid;
     uint32_t ret = 0;
     uint32_t cpuid_1_edx;
+    uint64_t bitmask;
 
     cpuid = get_supported_cpuid(s);
 
@@ -404,6 +406,25 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
         if (!has_msr_arch_capabs) {
             ret &= ~CPUID_7_0_EDX_ARCH_CAPABILITIES;
         }
+    } else if (function == 0xd && index == 0 &&
+               (reg == R_EAX || reg == R_EDX)) {
+        struct kvm_device_attr attr = {
+            .group = 0,
+            .attr = KVM_X86_XCOMP_GUEST_SUPP,
+            .addr = (unsigned long) &bitmask
+        };
+
+        bool sys_attr = kvm_check_extension(s, KVM_CAP_SYS_ATTRIBUTES);
+        if (!sys_attr) {
+            warn_report("cannot get sys attribute capabilities %d", sys_attr);
+        }
+
+        int rc = kvm_ioctl(s, KVM_GET_DEVICE_ATTR, &attr);
+        if (rc == -1 && (errno == ENXIO || errno == EINVAL)) {
+            warn_report("KVM_GET_DEVICE_ATTR(0, KVM_X86_XCOMP_GUEST_SUPP) "
+                        "error: %d", rc);
+        }
+        ret = (reg == R_EAX) ? bitmask : bitmask >> 32;
     } else if (function == 0x80000001 && reg == R_ECX) {
         /*
          * It's safe to enable TOPOEXT even if it's not returned by
@@ -5054,3 +5075,39 @@ bool kvm_arch_cpu_check_are_resettable(void)
 {
     return !sev_es_enabled();
 }
+
+#define ARCH_REQ_XCOMP_GUEST_PERM       0x1025
+
+void kvm_request_xsave_components(X86CPU *cpu, uint64_t mask)
+{
+    KVMState *s = kvm_state;
+    uint64_t supported;
+
+    mask &= XSTATE_DYNAMIC_MASK;
+    if (!mask) {
+        return;
+    }
+    /*
+     * Just ignore bits that are not in CPUID[EAX=0xD,ECX=0].
+     * ARCH_REQ_XCOMP_GUEST_PERM would fail, and QEMU has warned
+     * about them already because they are not supported features.
+     */
+    supported = kvm_arch_get_supported_cpuid(s, 0xd, 0, R_EAX);
+    supported |= (uint64_t)kvm_arch_get_supported_cpuid(s, 0xd, 0, R_EDX) << 32;
+    mask &= supported;
+
+    while (mask) {
+        int bit = ctz64(mask);
+        int rc = syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_GUEST_PERM, bit);
+        if (rc) {
+            /*
+             * Older kernel version (<5.17) do not support
+             * ARCH_REQ_XCOMP_GUEST_PERM, but also do not return
+             * any dynamic feature from kvm_arch_get_supported_cpuid.
+             */
+            warn_report("prctl(ARCH_REQ_XCOMP_GUEST_PERM) failure "
+                        "for feature bit %d", bit);
+        }
+        mask &= ~BIT_ULL(bit);
+    }
+}
diff --git a/target/i386/kvm/kvm_i386.h b/target/i386/kvm/kvm_i386.h
index a978509d50..4124912c20 100644
--- a/target/i386/kvm/kvm_i386.h
+++ b/target/i386/kvm/kvm_i386.h
@@ -52,5 +52,6 @@ bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp);
 uint64_t kvm_swizzle_msi_ext_dest_id(uint64_t address);
 
 bool kvm_enable_sgx_provisioning(KVMState *s);
+void kvm_request_xsave_components(X86CPU *cpu, uint64_t mask);
 
 #endif
-- 
2.35.3