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[PATCH] kvm: i386: allow TSC to differ by NTP correction bounds without TSC scaling

Marcelo Tosatti posted 1 patch 3 years, 11 months ago
Test FreeBSD passed
Test asan passed
Test docker-quick@centos7 passed
Test checkpatch passed
Test docker-mingw@fedora passed
Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/qemu tags/patchew/20200615120127.GB224592@fuller.cnet
Maintainers: Marcelo Tosatti <mtosatti@redhat.com>, Eduardo Habkost <ehabkost@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Richard Henderson <rth@twiddle.net>
There is a newer version of this series
[PATCH] kvm: i386: allow TSC to differ by NTP correction bounds without TSC scaling
Posted by Marcelo Tosatti 3 years, 11 months ago 

The Linux TSC calibration procedure is subject to small variations
(its common to see +-1 kHz difference between reboots on a given CPU, for example).

So migrating a guest between two hosts with identical processor can fail, in case 
of a small variation in calibrated TSC between them.

Allow a conservative 250ppm error between host TSC and VM TSC frequencies,
rather than requiring an exact match. NTP daemon in the guest can
correct this difference.

Also change migration to accept this bound.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index 34f8387..257fee4 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -739,23 +739,44 @@ static int kvm_arch_set_tsc_khz(CPUState *cs)
 {
     X86CPU *cpu = X86_CPU(cs);
     CPUX86State *env = &cpu->env;
-    int r;
+    int r, cur_freq;
+    bool set_ioctl = false;
 
     if (!env->tsc_khz) {
         return 0;
     }
 
-    r = kvm_check_extension(cs->kvm_state, KVM_CAP_TSC_CONTROL) ?
+    cur_freq = kvm_check_extension(cs->kvm_state, KVM_CAP_GET_TSC_KHZ) ?
+               kvm_vcpu_ioctl(cs, KVM_GET_TSC_KHZ) : -ENOTSUP;
+
+    /*
+     * If TSC scaling is supported, attempt to set TSC frequency.
+     */
+    if (kvm_check_extension(cs->kvm_state, KVM_CAP_TSC_CONTROL)) {
+        set_ioctl = true;
+    }
+
+    /*
+     * If desired TSC frequency is within bounds of NTP correction,
+     * attempt to set TSC frequency.
+     */
+    if (cur_freq != -ENOTSUP && freq_within_bounds(cur_freq, env->tsc_khz)) {
+        set_ioctl = true;
+    }
+
+    r = set_ioctl ?
         kvm_vcpu_ioctl(cs, KVM_SET_TSC_KHZ, env->tsc_khz) :
         -ENOTSUP;
+
     if (r < 0) {
         /* When KVM_SET_TSC_KHZ fails, it's an error only if the current
          * TSC frequency doesn't match the one we want.
          */
-        int cur_freq = kvm_check_extension(cs->kvm_state, KVM_CAP_GET_TSC_KHZ) ?
-                       kvm_vcpu_ioctl(cs, KVM_GET_TSC_KHZ) :
-                       -ENOTSUP;
-        if (cur_freq <= 0 || cur_freq != env->tsc_khz) {
+        cur_freq = kvm_check_extension(cs->kvm_state, KVM_CAP_GET_TSC_KHZ) ?
+                   kvm_vcpu_ioctl(cs, KVM_GET_TSC_KHZ) :
+                   -ENOTSUP;
+        if (cur_freq <= 0 || (cur_freq != env->tsc_khz &&
+                              !freq_within_bounds(cur_freq, env->tsc_khz))) {
             warn_report("TSC frequency mismatch between "
                         "VM (%" PRId64 " kHz) and host (%d kHz), "
                         "and TSC scaling unavailable",
diff --git a/target/i386/kvm_i386.h b/target/i386/kvm_i386.h
index 00bde7a..ebf9a64 100644
--- a/target/i386/kvm_i386.h
+++ b/target/i386/kvm_i386.h
@@ -47,4 +47,20 @@ bool kvm_has_x2apic_api(void);
 
 bool kvm_hv_vpindex_settable(void);
 
+/*
+ * Check whether target_freq is within conservative
+ * ntp correctable bounds (250ppm) of freq
+ */
+static inline bool freq_within_bounds(int freq, int target_freq)
+{
+        int max_freq = freq + (freq * 250 / 1000000);
+        int min_freq = freq - (freq * 250 / 1000000);
+
+        if (target_freq >= min_freq && target_freq <= max_freq) {
+                return true;
+        }
+
+        return false;
+}
+
 #endif
diff --git a/target/i386/machine.c b/target/i386/machine.c
index 0c96531..b052654 100644
--- a/target/i386/machine.c
+++ b/target/i386/machine.c
@@ -300,7 +300,7 @@ static int cpu_post_load(void *opaque, int version_id)
     int i;
 
     if (env->tsc_khz && env->user_tsc_khz &&
-        env->tsc_khz != env->user_tsc_khz) {
+        !freq_within_bounds(env->tsc_khz, env->user_tsc_khz)) {
         error_report("Mismatch between user-specified TSC frequency and "
                      "migrated TSC frequency");
         return -EINVAL;
[PATCH v2] kvm: i386: allow TSC to differ by NTP correction bounds without TSC scaling
Posted by Marcelo Tosatti 3 years, 11 months ago 

The Linux TSC calibration procedure is subject to small variations
(its common to see +-1 kHz difference between reboots on a given CPU, for example).

So migrating a guest between two hosts with identical processor can fail, in case 
of a small variation in calibrated TSC between them.

Allow a conservative 250ppm error between host TSC and VM TSC frequencies,
rather than requiring an exact match. NTP daemon in the guest can
correct this difference.

Also change migration to accept this bound.

KVM_SET_TSC_KHZ depends on a kernel interface change. Without this change,
the behaviour remains the same: in case of a different frequency 
between host and VM, KVM_SET_TSC_KHZ will fail and QEMU will exit.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

---

v2: ensure behaviour is unchanged for older kernels and
    improve changelogs (Paolo)

diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index 34f8387..ad825b1 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -735,26 +735,62 @@ static bool hyperv_enabled(X86CPU *cpu)
          cpu->hyperv_features || cpu->hyperv_passthrough);
 }
 
+/*
+ * Check whether target_freq is within conservative
+ * ntp correctable bounds (250ppm) of freq
+ */
+static inline bool freq_within_bounds(int freq, int target_freq)
+{
+        int max_freq = freq + (freq * 250 / 1000000);
+        int min_freq = freq - (freq * 250 / 1000000);
+
+        if (target_freq >= min_freq && target_freq <= max_freq) {
+                return true;
+        }
+
+        return false;
+}
+
 static int kvm_arch_set_tsc_khz(CPUState *cs)
 {
     X86CPU *cpu = X86_CPU(cs);
     CPUX86State *env = &cpu->env;
-    int r;
+    int r, cur_freq;
+    bool set_ioctl = false;
 
     if (!env->tsc_khz) {
         return 0;
     }
 
-    r = kvm_check_extension(cs->kvm_state, KVM_CAP_TSC_CONTROL) ?
+    cur_freq = kvm_check_extension(cs->kvm_state, KVM_CAP_GET_TSC_KHZ) ?
+               kvm_vcpu_ioctl(cs, KVM_GET_TSC_KHZ) : -ENOTSUP;
+
+    /*
+     * If TSC scaling is supported, attempt to set TSC frequency.
+     */
+    if (kvm_check_extension(cs->kvm_state, KVM_CAP_TSC_CONTROL)) {
+        set_ioctl = true;
+    }
+
+    /*
+     * If desired TSC frequency is within bounds of NTP correction,
+     * attempt to set TSC frequency.
+     */
+    if (cur_freq != -ENOTSUP && freq_within_bounds(cur_freq, env->tsc_khz)) {
+        set_ioctl = true;
+    }
+
+    r = set_ioctl ?
         kvm_vcpu_ioctl(cs, KVM_SET_TSC_KHZ, env->tsc_khz) :
         -ENOTSUP;
+
     if (r < 0) {
         /* When KVM_SET_TSC_KHZ fails, it's an error only if the current
          * TSC frequency doesn't match the one we want.
          */
-        int cur_freq = kvm_check_extension(cs->kvm_state, KVM_CAP_GET_TSC_KHZ) ?
-                       kvm_vcpu_ioctl(cs, KVM_GET_TSC_KHZ) :
-                       -ENOTSUP;
+        cur_freq = kvm_check_extension(cs->kvm_state, KVM_CAP_GET_TSC_KHZ) ?
+                   kvm_vcpu_ioctl(cs, KVM_GET_TSC_KHZ) :
+                   -ENOTSUP;
         if (cur_freq <= 0 || cur_freq != env->tsc_khz) {
             warn_report("TSC frequency mismatch between "
                         "VM (%" PRId64 " kHz) and host (%d kHz), "
Re: [PATCH v2] kvm: i386: allow TSC to differ by NTP correction bounds without TSC scaling
Posted by no-reply@patchew.org 3 years, 11 months ago 
Patchew URL: https://patchew.org/QEMU/20200616165805.GA324612@fuller.cnet/



Hi,

This series failed the asan build test. Please find the testing commands and
their output below. If you have Docker installed, you can probably reproduce it
locally.

=== TEST SCRIPT BEGIN ===
#!/bin/bash
export ARCH=x86_64
make docker-image-fedora V=1 NETWORK=1
time make docker-test-debug@fedora TARGET_LIST=x86_64-softmmu J=14 NETWORK=1
=== TEST SCRIPT END ===

  GEN     tools/virtiofsd/50-qemu-virtiofsd.json
  CC      contrib/vhost-user-input/main.o
  LINK    tests/qemu-iotests/socket_scm_helper
/usr/bin/ld: /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors_vfork.S.o): warning: common of `__interception::real_vfork' overridden by definition from /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors.cpp.o)
  GEN     docs/interop/qemu-qmp-ref.html
  GEN     docs/interop/qemu-qmp-ref.txt
  GEN     docs/interop/qemu-qmp-ref.7
---
  AR      libqemuutil.a
  LINK    elf2dmp
  CC      qemu-img.o
/usr/bin/ld: /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors_vfork.S.o): warning: common of `__interception::real_vfork' overridden by definition from /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors.cpp.o)
  LINK    qemu-io
/usr/bin/ld: /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors_vfork.S.o): warning: common of `__interception::real_vfork' overridden by definition from /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors.cpp.o)
  LINK    qemu-edid
  BUILD   pc-bios/optionrom/linuxboot_dma.img
  BUILD   pc-bios/optionrom/pvh.img
---
  BUILD   pc-bios/optionrom/pvh.raw
  SIGN    pc-bios/optionrom/pvh.bin
  LINK    fsdev/virtfs-proxy-helper
/usr/bin/ld: /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors_vfork.S.o): warning: common of `__interception::real_vfork' overridden by definition from /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors.cpp.o)
  LINK    scsi/qemu-pr-helper
/usr/bin/ld: /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors_vfork.S.o): warning: common of `__interception::real_vfork' overridden by definition from /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors.cpp.o)
  LINK    qemu-bridge-helper
/usr/bin/ld: /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors_vfork.S.o): warning: common of `__interception::real_vfork' overridden by definition from /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors.cpp.o)
  AR      libvhost-user.a
/usr/bin/ld: /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors_vfork.S.o): warning: common of `__interception::real_vfork' overridden by definition from /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors.cpp.o)
  GEN     docs/interop/qemu-ga-ref.html
  GEN     docs/interop/qemu-ga-ref.txt
  GEN     docs/interop/qemu-ga-ref.7
  LINK    qemu-keymap
/usr/bin/ld: /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors_vfork.S.o): warning: common of `__interception::real_vfork' overridden by definition from /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors.cpp.o)
  LINK    ivshmem-client
  LINK    ivshmem-server
/usr/bin/ld: /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors_vfork.S.o): warning: common of `__interception::real_vfork' overridden by definition from /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors.cpp.o)
/usr/bin/ld: /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors_vfork.S.o): warning: common of `__interception::real_vfork' overridden by definition from /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors.cpp.o)
  LINK    qemu-nbd
/usr/bin/ld: /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors_vfork.S.o): warning: common of `__interception::real_vfork' overridden by definition from /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors.cpp.o)
  LINK    qemu-storage-daemon
  LINK    virtiofsd
  LINK    vhost-user-input
  LINK    qemu-ga
/usr/bin/ld: /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors_vfork.S.o): warning: common of `__interception::real_vfork' overridden by definition from /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors.cpp.o)
/usr/bin/ld: /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors_vfork.S.o): warning: common of `__interception::real_vfork' overridden by definition from /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors.cpp.o)
/usr/bin/ld: /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors_vfork.S.o): warning: common of `__interception::real_vfork' overridden by definition from /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors.cpp.o)
/usr/bin/ld: /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors_vfork.S.o): warning: common of `__interception::real_vfork' overridden by definition from /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors.cpp.o)
  LINK    qemu-img
/usr/bin/ld: /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors_vfork.S.o): warning: common of `__interception::real_vfork' overridden by definition from /usr/lib64/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors.cpp.o)
  GEN     x86_64-softmmu/hmp-commands.h
  GEN     x86_64-softmmu/hmp-commands-info.h
  GEN     x86_64-softmmu/config-devices.h
---
  CC      x86_64-softmmu/qtest.o
  CC      x86_64-softmmu/memory.o
  CC      x86_64-softmmu/memory_mapping.o
/tmp/qemu-test/src/fpu/softfloat.c:3365:13: error: bitwise negation of a boolean expression; did you mean logical negation? [-Werror,-Wbool-operation]
    absZ &= ~ ( ( ( roundBits ^ 0x40 ) == 0 ) & roundNearestEven );
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            !
/tmp/qemu-test/src/fpu/softfloat.c:3423:18: error: bitwise negation of a boolean expression; did you mean logical negation? [-Werror,-Wbool-operation]
        absZ0 &= ~ ( ( (uint64_t) ( absZ1<<1 ) == 0 ) & roundNearestEven );
                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                 !
/tmp/qemu-test/src/fpu/softfloat.c:3483:18: error: bitwise negation of a boolean expression; did you mean logical negation? [-Werror,-Wbool-operation]
        absZ0 &= ~(((uint64_t)(absZ1<<1) == 0) & roundNearestEven);
                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                 !
/tmp/qemu-test/src/fpu/softfloat.c:3606:13: error: bitwise negation of a boolean expression; did you mean logical negation? [-Werror,-Wbool-operation]
    zSig &= ~ ( ( ( roundBits ^ 0x40 ) == 0 ) & roundNearestEven );
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            !
/tmp/qemu-test/src/fpu/softfloat.c:3760:13: error: bitwise negation of a boolean expression; did you mean logical negation? [-Werror,-Wbool-operation]
    zSig &= ~ ( ( ( roundBits ^ 0x200 ) == 0 ) & roundNearestEven );
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            !
/tmp/qemu-test/src/fpu/softfloat.c:3987:21: error: bitwise negation of a boolean expression; did you mean logical negation? [-Werror,-Wbool-operation]
                    ~ ( ( (uint64_t) ( zSig1<<1 ) == 0 ) & roundNearestEven );
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                    !
/tmp/qemu-test/src/fpu/softfloat.c:4003:22: error: bitwise negation of a boolean expression; did you mean logical negation? [-Werror,-Wbool-operation]
            zSig0 &= ~ ( ( (uint64_t) ( zSig1<<1 ) == 0 ) & roundNearestEven );
                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                     !
/tmp/qemu-test/src/fpu/softfloat.c:4273:18: error: bitwise negation of a boolean expression; did you mean logical negation? [-Werror,-Wbool-operation]
        zSig1 &= ~ ( ( zSig2 + zSig2 == 0 ) & roundNearestEven );
                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                 !
8 errors generated.
make[1]: *** [/tmp/qemu-test/src/rules.mak:69: fpu/softfloat.o] Error 1
make[1]: *** Waiting for unfinished jobs....
make: *** [Makefile:527: x86_64-softmmu/all] Error 2
Traceback (most recent call last):
  File "./tests/docker/docker.py", line 669, in <module>
    sys.exit(main())
---
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['sudo', '-n', 'docker', 'run', '--label', 'com.qemu.instance.uuid=b4a5184fc16644b0914afc022957a9c0', '-u', '1001', '--security-opt', 'seccomp=unconfined', '--rm', '-e', 'TARGET_LIST=x86_64-softmmu', '-e', 'EXTRA_CONFIGURE_OPTS=', '-e', 'V=', '-e', 'J=14', '-e', 'DEBUG=', '-e', 'SHOW_ENV=', '-e', 'CCACHE_DIR=/var/tmp/ccache', '-v', '/home/patchew/.cache/qemu-docker-ccache:/var/tmp/ccache:z', '-v', '/var/tmp/patchew-tester-tmp-zgpzucz9/src/docker-src.2020-06-16-17.29.39.13804:/var/tmp/qemu:z,ro', 'qemu:fedora', '/var/tmp/qemu/run', 'test-debug']' returned non-zero exit status 2.
filter=--filter=label=com.qemu.instance.uuid=b4a5184fc16644b0914afc022957a9c0
make[1]: *** [docker-run] Error 1
make[1]: Leaving directory `/var/tmp/patchew-tester-tmp-zgpzucz9/src'
make: *** [docker-run-test-debug@fedora] Error 2

real    6m19.842s
user    0m8.530s


The full log is available at
http://patchew.org/logs/20200616165805.GA324612@fuller.cnet/testing.asan/?type=message.
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