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Re: [Qemu-devel] [PATCH] target-i386: add AMD CPUID.1:edx aliases to x86
From: |
Eduardo Habkost |
Subject: |
Re: [Qemu-devel] [PATCH] target-i386: add AMD CPUID.1:edx aliases to x86_cpu_get_migratable_flags |
Date: |
Fri, 15 Apr 2016 13:54:27 -0300 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Thu, Apr 14, 2016 at 10:55:07PM +0200, Radim Krčmář wrote:
> QEMU complains about -cpu host on an AMD machine:
> warning: host doesn't support requested feature: CPUID.80000001H:EDX [bit 0]
> For bits 0,1,3,4,5,6,7,8,9,12,13,14,15,16,17,23,24.
>
> Host does support them, but x86_cpu_get_migratable_flags filters unnamed
> features and drops these bits without realizing that they are aliases to
> CPUID.1H:EDX and have their names there.
>
> See https://bugzilla.redhat.com/show_bug.cgi?id=1326721 for details.
>
> Signed-off-by: Radim Krčmář <address@hidden>
> ---
> target-i386/cpu.c | 40 ++++++++++++++++++++++------------------
> 1 file changed, 22 insertions(+), 18 deletions(-)
>
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index ddae932ee1b4..66bd9d0c4039 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -506,7 +506,7 @@ const char *get_register_name_32(unsigned int reg)
> * Returns the set of feature flags that are supported and migratable by
> * QEMU, for a given FeatureWord.
> */
> -static uint32_t x86_cpu_get_migratable_flags(FeatureWord w)
> +static uint32_t x86_cpu_get_migratable_flags(FeatureWord w, bool is_amd)
> {
> FeatureWordInfo *wi = &feature_word_info[w];
> uint32_t r = 0;
> @@ -514,12 +514,18 @@ static uint32_t
> x86_cpu_get_migratable_flags(FeatureWord w)
>
> for (i = 0; i < 32; i++) {
> uint32_t f = 1U << i;
> + FeatureWordInfo *effective_wi = wi;
> +
> + if (is_amd && w == FEAT_8000_0001_EDX && f & CPUID_EXT2_AMD_ALIASES)
> {
> + effective_wi = &feature_word_info[FEAT_1_EDX];
> + }
> +
> /* If the feature name is unknown, it is not supported by QEMU yet */
> - if (!wi->feat_names[i]) {
> + if (!effective_wi->feat_names[i]) {
> continue;
> }
> /* Skip features known to QEMU, but explicitly marked as
> unmigratable */
> - if (wi->unmigratable_flags & f) {
> + if (effective_wi->unmigratable_flags & f) {
> continue;
> }
> r |= f;
I don't think we need that complexity to fix the problem. We even
have a similar hack in kvm_arch_get_supported_cpuid() to make
sure it handles the alias bits properly. Instead of hacking those
functions to copy CPUID[1] data, it's much easier to simply copy
the alias bits in realizefn after we call
x86_cpu_filter_features(), not before.
The following (untested) fix should be sufficient:
diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index ddae932..d0b5b69 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -2897,6 +2897,14 @@ static void x86_cpu_realizefn(DeviceState *dev, Error
**errp)
env->cpuid_level = 7;
}
+ if (x86_cpu_filter_features(cpu) && cpu->enforce_cpuid) {
+ error_setg(&local_err,
+ kvm_enabled() ?
+ "Host doesn't support requested features" :
+ "TCG doesn't support requested features");
+ goto out;
+ }
+
/* On AMD CPUs, some CPUID[8000_0001].EDX bits must match the bits on
* CPUID[1].EDX.
*/
@@ -2907,14 +2915,6 @@ static void x86_cpu_realizefn(DeviceState *dev, Error
**errp)
}
- if (x86_cpu_filter_features(cpu) && cpu->enforce_cpuid) {
- error_setg(&local_err,
- kvm_enabled() ?
- "Host doesn't support requested features" :
- "TCG doesn't support requested features");
- goto out;
- }
-
#ifndef CONFIG_USER_ONLY
qemu_register_reset(x86_cpu_machine_reset_cb, cpu);
--
Eduardo