Re: [PATCH v8 05/55] i386/tdx: Get tdx_capabilities via KVM_TDX_CAPABILITIES

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 4/2/2025 7:00 PM, Daniel P. Berrangé wrote:
> On Tue, Apr 01, 2025 at 09:01:15AM -0400, Xiaoyao Li wrote:
>> KVM provides TDX capabilities via sub command KVM_TDX_CAPABILITIES of
>> IOCTL(KVM_MEMORY_ENCRYPT_OP). Get the capabilities when initializing
>> TDX context. It will be used to validate user's setting later.
>>
>> Since there is no interface reporting how many cpuid configs contains in
>> KVM_TDX_CAPABILITIES, QEMU chooses to try starting with a known number
>> and abort when it exceeds KVM_MAX_CPUID_ENTRIES.
>>
>> Besides, introduce the interfaces to invoke TDX "ioctls" at VCPU scope
>> in preparation.
>>
>> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
>> ---
>> Changes in v7:
>> - refine and unifiy the error handling; (Daniel)
>>
>> Changes in v6:
>> - Pass CPUState * to tdx_vcpu_ioctl();
>> - update commit message to remove platform scope thing;
>> - dump hw_error when it's non-zero to help debug;
>>
>> Changes in v4:
>> - use {} to initialize struct kvm_tdx_cmd, to avoid memset();
>> - remove tdx_platform_ioctl() because no user;
>>
>> Changes in v3:
>> - rename __tdx_ioctl() to tdx_ioctl_internal()
>> - Pass errp in get_tdx_capabilities();
>>
>> changes in v2:
>>    - Make the error message more clear;
>>
>> changes in v1:
>>    - start from nr_cpuid_configs = 6 for the loop;
>>    - stop the loop when nr_cpuid_configs exceeds KVM_MAX_CPUID_ENTRIES;
>> ---
>>   target/i386/kvm/kvm.c      |   2 -
>>   target/i386/kvm/kvm_i386.h |   2 +
>>   target/i386/kvm/tdx.c      | 107 ++++++++++++++++++++++++++++++++++++-
>>   3 files changed, 108 insertions(+), 3 deletions(-)
>>
>> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
>> index 1af4710556ad..b4fa35405fe1 100644
>> --- a/target/i386/kvm/kvm.c
>> +++ b/target/i386/kvm/kvm.c
>> @@ -1779,8 +1779,6 @@ static int hyperv_init_vcpu(X86CPU *cpu)
>>   
>>   static Error *invtsc_mig_blocker;
>>   
>> -#define KVM_MAX_CPUID_ENTRIES  100
>> -
>>   static void kvm_init_xsave(CPUX86State *env)
>>   {
>>       if (has_xsave2) {
>> diff --git a/target/i386/kvm/kvm_i386.h b/target/i386/kvm/kvm_i386.h
>> index 88565e8dbac1..ed1e61fb8ba9 100644
>> --- a/target/i386/kvm/kvm_i386.h
>> +++ b/target/i386/kvm/kvm_i386.h
>> @@ -13,6 +13,8 @@
>>   
>>   #include "system/kvm.h"
>>   
>> +#define KVM_MAX_CPUID_ENTRIES  100
>> +
>>   /* always false if !CONFIG_KVM */
>>   #define kvm_pit_in_kernel() \
>>       (kvm_irqchip_in_kernel() && !kvm_irqchip_is_split())
>> diff --git a/target/i386/kvm/tdx.c b/target/i386/kvm/tdx.c
>> index 4ff94860815d..c67be5e618e2 100644
>> --- a/target/i386/kvm/tdx.c
>> +++ b/target/i386/kvm/tdx.c
>> @@ -10,17 +10,122 @@
>>    */
>>   
>>   #include "qemu/osdep.h"
>> +#include "qemu/error-report.h"
>> +#include "qapi/error.h"
>>   #include "qom/object_interfaces.h"
>>   
>>   #include "hw/i386/x86.h"
>>   #include "kvm_i386.h"
>>   #include "tdx.h"
>>   
>> +static struct kvm_tdx_capabilities *tdx_caps;
>> +
>> +enum tdx_ioctl_level {
>> +    TDX_VM_IOCTL,
>> +    TDX_VCPU_IOCTL,
>> +};
>> +
>> +static int tdx_ioctl_internal(enum tdx_ioctl_level level, void *state,
>> +                              int cmd_id, __u32 flags, void *data,
>> +                              Error **errp)
>> +{
>> +    struct kvm_tdx_cmd tdx_cmd = {};
>> +    int r;
>> +
>> +    const char *tdx_ioctl_name[] = {
>> +        [KVM_TDX_CAPABILITIES] = "KVM_TDX_CAPABILITIES",
>> +        [KVM_TDX_INIT_VM] = "KVM_TDX_INIT_VM",
>> +        [KVM_TDX_INIT_VCPU] = "KVM_TDX_INIT_VCPU",
>> +        [KVM_TDX_INIT_MEM_REGION] = "KVM_TDX_INIT_MEM_REGION",
>> +        [KVM_TDX_FINALIZE_VM] = "KVM_TDX_FINALIZE_VM",
>> +        [KVM_TDX_GET_CPUID] = "KVM_TDX_GET_CPUID",
>> +    };
>> +
>> +    tdx_cmd.id = cmd_id;
>> +    tdx_cmd.flags = flags;
>> +    tdx_cmd.data = (__u64)(unsigned long)data;
>> +
>> +    switch (level) {
>> +    case TDX_VM_IOCTL:
>> +        r = kvm_vm_ioctl(kvm_state, KVM_MEMORY_ENCRYPT_OP, &tdx_cmd);
>> +        break;
>> +    case TDX_VCPU_IOCTL:
>> +        r = kvm_vcpu_ioctl(state, KVM_MEMORY_ENCRYPT_OP, &tdx_cmd);
>> +        break;
>> +    default:
>> +        error_setg(errp, "Invalid tdx_ioctl_level %d", level);
>> +        return -EINVAL;
>> +    }
>> +
>> +    if (r < 0) {
>> +        error_setg_errno(errp, -r, "TDX ioctl %s failed, hw_errors: 0x%llx",
>> +                         tdx_ioctl_name[cmd_id], tdx_cmd.hw_error);
>> +    }
>> +    return r;
>> +}
>> +
>> +static inline int tdx_vm_ioctl(int cmd_id, __u32 flags, void *data,
>> +                               Error **errp)
>> +{
>> +    return tdx_ioctl_internal(TDX_VM_IOCTL, NULL, cmd_id, flags, data, errp);
>> +}
>> +
>> +static inline int tdx_vcpu_ioctl(CPUState *cpu, int cmd_id, __u32 flags,
>> +                                 void *data, Error **errp)
>> +{
>> +    return  tdx_ioctl_internal(TDX_VCPU_IOCTL, cpu, cmd_id, flags, data, errp);
>> +}
>> +
>> +static int get_tdx_capabilities(Error **errp)
>> +{
>> +    struct kvm_tdx_capabilities *caps;
>> +    /* 1st generation of TDX reports 6 cpuid configs */
>> +    int nr_cpuid_configs = 6;
>> +    size_t size;
>> +    int r;
>> +
>> +    do {
>> +        Error *local_err = NULL;
>> +        size = sizeof(struct kvm_tdx_capabilities) +
>> +                      nr_cpuid_configs * sizeof(struct kvm_cpuid_entry2);
>> +        caps = g_malloc0(size);
>> +        caps->cpuid.nent = nr_cpuid_configs;
>> +
>> +        r = tdx_vm_ioctl(KVM_TDX_CAPABILITIES, 0, caps, &local_err);
>> +        if (r == -E2BIG) {
>> +            g_free(caps);
>> +            nr_cpuid_configs *= 2;
>> +            if (nr_cpuid_configs > KVM_MAX_CPUID_ENTRIES) {
>> +                error_report("KVM TDX seems broken that number of CPUID entries"
>> +                             " in kvm_tdx_capabilities exceeds limit: %d",
>> +                             KVM_MAX_CPUID_ENTRIES);
>> +                error_propagate(errp, local_err);
>> +                return r;
>> +            }
>> +            error_free(local_err);
> 
> IIRC, you'll need  'local_err = NULL' here, otherwise next time around
> the loop 'local_err' will be pointing to a free'd error object which
> 'error_setg' will think is still valid & won't overwrite.

it's set to NULL at the beginning of the do loop.

(It looks I need to declare Error *local_err outside the do loop.)

>> +        } else if (r < 0) {
>> +            g_free(caps);
>> +            error_propagate(errp, local_err);
>> +            return r;
>> +        }
>> +    } while (r == -E2BIG);
>> +
>> +    tdx_caps = caps;
>> +
>> +    return 0;
>> +}
>> +
> 
> 
> With regards,
> Daniel