Re: [PATCH v6 05/60] i386/tdx: Get tdx_capabilities via KVM_TDX_CAPABILITIES

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Nov 05, 2024 at 01:23:13AM -0500, 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 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      | 93 +++++++++++++++++++++++++++++++++++++-
>  3 files changed, 94 insertions(+), 3 deletions(-)
> 
> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> index 2bbac603da70..b843de7f2379 100644
> --- a/target/i386/kvm/kvm.c
> +++ b/target/i386/kvm/kvm.c
> @@ -1782,8 +1782,6 @@ 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 9de9c0d30388..7ac4c3a91171 100644
> --- a/target/i386/kvm/kvm_i386.h
> +++ b/target/i386/kvm/kvm_i386.h
> @@ -13,6 +13,8 @@
>  
>  #include "sysemu/kvm.h"
>  
> +#define KVM_MAX_CPUID_ENTRIES  100
> +
>  #ifdef CONFIG_KVM
>  
>  #define kvm_pit_in_kernel() \
> diff --git a/target/i386/kvm/tdx.c b/target/i386/kvm/tdx.c
> index 85f006c1d6b4..907044910fec 100644
> --- a/target/i386/kvm/tdx.c
> +++ b/target/i386/kvm/tdx.c
> @@ -12,17 +12,108 @@
>   */
>  
>  #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)
> +{
> +    struct kvm_tdx_cmd tdx_cmd = {};
> +    int r;
> +
> +    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_report("Invalid tdx_ioctl_level %d", level);
> +        exit(1);
> +    }
> +
> +    if (r && tdx_cmd.hw_error) {
> +        error_report("TDX ioctl %d return with %d, hw_errors: 0x%llx",
> +                     cmd_id, r, tdx_cmd.hw_error);
> +    }
> +    return r;
> +}

I feel like the error handling of this method is rather inconsistent.
In one place we error_report() and then exit(), in another place
we error_report() but return, and in another place we report nothing
at all. When we return, the caller propagates an Error **errp object,
but this propagated message lacks the potentially useful 'hw_errors'
info.

IMHO this method ought to have an 'Error **errp' parameter and always
fill it & propagate. Let the caller decide whether to exit or not.

If you continue returning 'r', then the caller can still handle
E2BIG, discarding the 'Error' object in that case.


> +
> +static inline int tdx_vm_ioctl(int cmd_id, __u32 flags, void *data)
> +{
> +    return tdx_ioctl_internal(TDX_VM_IOCTL, NULL, cmd_id, flags, data);
> +}
> +
> +static inline int tdx_vcpu_ioctl(CPUState *cpu, int cmd_id, __u32 flags,
> +                                 void *data)
> +{
> +    return  tdx_ioctl_internal(TDX_VCPU_IOCTL, cpu, cmd_id, flags, data);
> +}
> +
> +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 {
> +        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);
> +        if (r == -E2BIG) {
> +            g_free(caps);
> +            nr_cpuid_configs *= 2;
> +            if (nr_cpuid_configs > KVM_MAX_CPUID_ENTRIES) {
> +                error_setg(errp, "%s: KVM TDX seems broken that number of CPUID"
> +                           " entries in kvm_tdx_capabilities exceeds limit %d",
> +                           __func__, KVM_MAX_CPUID_ENTRIES);
> +                return r;
> +            }
> +        } else if (r < 0) {
> +            g_free(caps);
> +            error_setg_errno(errp, -r, "%s: KVM_TDX_CAPABILITIES failed", __func__);
> +            return r;
> +        }
> +    } while (r == -E2BIG);
> +
> +    tdx_caps = caps;
> +
> +    return 0;
> +}
> +
>  static int tdx_kvm_init(ConfidentialGuestSupport *cgs, Error **errp)
>  {
> +    int r = 0;
> +
>      kvm_mark_guest_state_protected();
>  
> -    return 0;
> +    if (!tdx_caps) {
> +        r = get_tdx_capabilities(errp);
> +    }
> +
> +    return r;
>  }
>  
>  static int tdx_kvm_type(X86ConfidentialGuest *cg)
> -- 
> 2.34.1
> 

With regards,
Daniel
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