Re: [PATCH v2] target/i386/hvf: add vmware-cpuid-freq cpu feature

[Roman Bolshakov <r.bolshakov@yadro.com>]

On Thu, Jan 14, 2021 at 10:47:03PM +0300, yaroshchuk2000@gmail.com wrote:
> From: Vladislav Yaroshchuk <yaroshchuk2000@gmail.com>
> 
> For `-accel hvf` cpu_x86_cpuid() is wrapped with hvf_cpu_x86_cpuid() to
> add paravirtualization cpuid leaf 0x40000010
> https://lkml.org/lkml/2008/10/1/246
> 
> Leaf 0x40000010, Timing Information:
> EAX: (Virtual) TSC frequency in kHz.
> EBX: (Virtual) Bus (local apic timer) frequency in kHz.
> ECX, EDX: RESERVED (Per above, reserved fields are set to zero).
> 
> On macOS TSC and APIC Bus frequencies can be readed by sysctl call with
> names `machdep.tsc.frequency` and `hw.busfrequency`
> 
> This options is required for Darwin-XNU guest to be synchronized with
> host
> 
> Signed-off-by: Vladislav Yaroshchuk <yaroshchuk2000@gmail.com>
> ---
>  target/i386/hvf/hvf.c | 90 ++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 89 insertions(+), 1 deletion(-)
> 
> diff --git a/target/i386/hvf/hvf.c b/target/i386/hvf/hvf.c
> index ed9356565c..a5daafe202 100644
> --- a/target/i386/hvf/hvf.c
> +++ b/target/i386/hvf/hvf.c
> @@ -65,6 +65,7 @@
>  
>  #include <Hypervisor/hv.h>
>  #include <Hypervisor/hv_vmx.h>
> +#include <sys/sysctl.h>
>  
>  #include "exec/address-spaces.h"
>  #include "hw/i386/apic_internal.h"
> @@ -456,6 +457,48 @@ static void dummy_signal(int sig)
>  {
>  }
>  
> +static void init_tsc_freq(CPUX86State *env)
> +{
> +    size_t length;
> +    uint64_t tsc_freq;
> +
> +    if (env->tsc_khz != 0) {
> +        return;
> +    }
> +
> +    length = sizeof(uint64_t);
> +    if (sysctlbyname("machdep.tsc.frequency", &tsc_freq, &length, NULL, 0)) {
> +        return;
> +    }
> +    env->tsc_khz = tsc_freq / 1000;  /* Hz to KHz */
> +}
> +
> +static void init_apic_bus_freq(CPUX86State *env)
> +{
> +    size_t length;
> +    uint64_t bus_freq;
> +
> +    if (env->apic_bus_freq != 0) {
> +        return;
> +    }
> +
> +    length = sizeof(uint64_t);
> +    if (sysctlbyname("hw.busfrequency", &bus_freq, &length, NULL, 0)) {
> +        return;
> +    }
> +    env->apic_bus_freq = bus_freq;
> +}
> +
> +static inline bool tsc_is_known(CPUX86State *env)
> +{
> +    return env->tsc_khz != 0;
> +}
> +
> +static inline bool apic_bus_freq_is_known(CPUX86State *env)
> +{
> +    return env->apic_bus_freq != 0;
> +}
> +
>  int hvf_init_vcpu(CPUState *cpu)
>  {
>  
> @@ -480,6 +523,15 @@ int hvf_init_vcpu(CPUState *cpu)
>      hvf_state->hvf_caps = g_new0(struct hvf_vcpu_caps, 1);
>      env->hvf_mmio_buf = g_new(char, 4096);
>  
> +    if (x86cpu->vmware_cpuid_freq) {
> +        init_tsc_freq(env);
> +        init_apic_bus_freq(env);
> +
> +        if (!tsc_is_known(env) || !apic_bus_freq_is_known(env)) {
> +            error_report("vmware-cpuid-freq: feature couldn't be enabled");
> +        }
> +    }
> +
>      r = hv_vcpu_create((hv_vcpuid_t *)&cpu->hvf_fd, HV_VCPU_DEFAULT);
>      cpu->vcpu_dirty = 1;
>      assert_hvf_ok(r);
> @@ -597,6 +649,42 @@ static void hvf_store_events(CPUState *cpu, uint32_t ins_len, uint64_t idtvec_in
>      }
>  }
>  
> +static void hvf_cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
> +                              uint32_t *eax, uint32_t *ebx,
> +                              uint32_t *ecx, uint32_t *edx)
> +{
> +    /*
> +     * A wrapper extends cpu_x86_cpuid with 0x40000000 and 0x40000010 leafs
> +     * Provides vmware-cpuid-freq support to hvf
> +     */
> +
> +    uint32_t signature[3];
> +
> +    if (!tsc_is_known(env) || !apic_bus_freq_is_known(env)) {
> +        cpu_x86_cpuid(env, index, count, eax, ebx, ecx, edx);
> +        return;
> +    }
> +
> +    switch (index) {
> +    case 0x40000000:
> +        memcpy(signature, "TCGTCGTCGTCG", 12); /* QEMU Signature */

Hi Vladislav,

TCG belongs to TCG accel identification, for HVF it should be
HVFHVFHVFHVF.

> +        *eax = 0x40000010;                     /* Max available cpuid leaf */
> +        *ebx = signature[0];
> +        *ecx = signature[1];
> +        *edx = signature[2];

TCG and KVM don't report their identity unless kvm or tcg-cpuid
properties are set. I wonder if we need to guard it likewise?

But as of now QEMU is not consistent in that regard. Two parameters are
needed for KVM - kvm=on,vmware-cpuid-freq=on. vmware-cpuid-freq is
sufficient for WHPX but WHPX doesn't expose itself (ebx=ecx=edx=0). TCG
doesn't seem to support vmware-cpuid-freq but reports it's name only if
tcg-cpuid property is set.

> +        break;

CPUID for not implemented hypervisor-specific leafs from 0x40000001 up
to 0x4000000f should be all zeroes but cpu_x86_cpuid() only returns zero
values for 0x40000001. Likely, you need to reset return values for the
leafs here or in cpu_x86_cpuid(). In the latter case you'll also fix a
similar bug in WHPX accel.

Otherwise, looks good.

Thanks,
Roman

> +    case 0x40000010:
> +        *eax = env->tsc_khz;
> +        *ebx = env->apic_bus_freq / 1000; /* Hz to KHz */
> +        *ecx = 0;
> +        *edx = 0;
> +        break;
> +    default:
> +        cpu_x86_cpuid(env, index, count, eax, ebx, ecx, edx);
> +        break;
> +    }
> +}
> +
>  int hvf_vcpu_exec(CPUState *cpu)
>  {
>      X86CPU *x86_cpu = X86_CPU(cpu);
> @@ -734,7 +822,7 @@ int hvf_vcpu_exec(CPUState *cpu)
>              uint32_t rcx = (uint32_t)rreg(cpu->hvf_fd, HV_X86_RCX);
>              uint32_t rdx = (uint32_t)rreg(cpu->hvf_fd, HV_X86_RDX);
>  
> -            cpu_x86_cpuid(env, rax, rcx, &rax, &rbx, &rcx, &rdx);
> +            hvf_cpu_x86_cpuid(env, rax, rcx, &rax, &rbx, &rcx, &rdx);
>  
>              wreg(cpu->hvf_fd, HV_X86_RAX, rax);
>              wreg(cpu->hvf_fd, HV_X86_RBX, rbx);
> -- 
> 2.28.0
>