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target/i386: Fix conditional CONFIG_SYNDBG enablement 

Putting HYPERV_FEAT_SYNDBG entry under "#ifdef CONFIG_SYNDBG" in
'kvm_hyperv_properties' array is wrong: as HYPERV_FEAT_SYNDBG is not
the highest feature number, the result is an empty (zeroed) entry in
the array (and not a skipped entry!). hyperv_feature_supported() is
designed to check that all CPUID bits are set but for a zeroed
feature in 'kvm_hyperv_properties' it returns 'true' so QEMU considers
HYPERV_FEAT_SYNDBG as always supported, regardless of whether KVM host
actually supports it.

To fix the issue, leave HYPERV_FEAT_SYNDBG's definition in
'kvm_hyperv_properties' array, there's nothing wrong in having it defined
even when 'CONFIG_SYNDBG' is not set. Instead, put "hv-syndbg" CPU property
under '#ifdef CONFIG_SYNDBG' to alter the existing behavior when the flag
is silently skipped in !CONFIG_SYNDBG builds.

Leave an 'assert' sentinel in hyperv_feature_supported() making sure there
are no 'holes' or improperly defined features in 'kvm_hyperv_properties'.

Fixes: d8701185f4 ("hw: hyperv: Initial commit for Synthetic Debugging device")
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Link: https://lore.kernel.org/r/20240917160051.2637594-2-vkuznets@redhat.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Vitaly Kuznetsov 2024-09-17 18:00:48 +02:00 committed by Paolo Bonzini
parent b5151ace58
commit bbf3810f2c
2 changed files with 9 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
target/i386/cpu.c
View File

@ -8299,8 +8299,10 @@ static Property x86_cpu_properties[] = {
HYPERV_FEAT_TLBFLUSH_DIRECT, 0),
DEFINE_PROP_ON_OFF_AUTO("hv-no-nonarch-coresharing", X86CPU,
hyperv_no_nonarch_cs, ON_OFF_AUTO_OFF),
#ifdef CONFIG_SYNDBG
DEFINE_PROP_BIT64("hv-syndbg", X86CPU, hyperv_features,
HYPERV_FEAT_SYNDBG, 0),
#endif
DEFINE_PROP_BOOL("hv-passthrough", X86CPU, hyperv_passthrough, false),
DEFINE_PROP_BOOL("hv-enforce-cpuid", X86CPU, hyperv_enforce_cpuid, false),

11
target/i386/kvm/kvm.c
View File

@ -1056,7 +1056,6 @@ static struct {
.bits = HV_DEPRECATING_AEOI_RECOMMENDED}
}
},
#ifdef CONFIG_SYNDBG
[HYPERV_FEAT_SYNDBG] = {
.desc = "Enable synthetic kernel debugger channel (hv-syndbg)",
.flags = {
@ -1065,7 +1064,6 @@ static struct {
},
.dependencies = BIT(HYPERV_FEAT_SYNIC) | BIT(HYPERV_FEAT_RELAXED)
},
#endif
[HYPERV_FEAT_MSR_BITMAP] = {
.desc = "enlightened MSR-Bitmap (hv-emsr-bitmap)",
.flags = {
@ -1317,6 +1315,13 @@ static bool hyperv_feature_supported(CPUState *cs, int feature)
uint32_t func, bits;
int i, reg;
/*
* kvm_hyperv_properties needs to define at least one CPUID flag which
* must be used to detect the feature, it's hard to say whether it is
* supported or not otherwise.
*/
assert(kvm_hyperv_properties[feature].flags[0].func);
for (i = 0; i < ARRAY_SIZE(kvm_hyperv_properties[feature].flags); i++) {
func = kvm_hyperv_properties[feature].flags[i].func;
@ -4025,13 +4030,11 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
kvm_msr_entry_add(cpu, HV_X64_MSR_TSC_EMULATION_STATUS,
env->msr_hv_tsc_emulation_status);
}
#ifdef CONFIG_SYNDBG
if (hyperv_feat_enabled(cpu, HYPERV_FEAT_SYNDBG) &&
has_msr_hv_syndbg_options) {
kvm_msr_entry_add(cpu, HV_X64_MSR_SYNDBG_OPTIONS,
hyperv_syndbg_query_options());
}
#endif
}
if (hyperv_feat_enabled(cpu, HYPERV_FEAT_VAPIC)) {
kvm_msr_entry_add(cpu, HV_X64_MSR_APIC_ASSIST_PAGE,