Re: [PATCH 5/7] KVM: TDX: Handle TDG.VP.VMCALL

Xiaoyao Li
2024-12-13T09:40:56Z

On 12/1/2024 11:53 AM, Binbin Wu wrote:
> Convert TDG.VP.VMCALL<ReportFatalError> to KVM_EXIT_SYSTEM_EVENT with
> a new type KVM_SYSTEM_EVENT_TDX_FATAL and forward it to userspace for
> handling.
>
> TD guest can use TDG.VP.VMCALL<ReportFatalError> to report the fatal
> error it has experienced. This hypercall is special because TD guest
> is requesting a termination with the error information, KVM needs to
> forward the hypercall to userspace anyway, KVM doesn't do sanity checks
> and let userspace decide what to do.
>
> Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
> ---
> Hypercalls exit to userspace breakout:
> - New added.
> Implement one of the hypercalls need to exit to userspace for handling after
> reverting "KVM: TDX: Add KVM Exit for TDX TDG.VP.VMCALL", which tries to resolve
> Sean's comment.
> https://lore.kernel.org/kvm/Zg18ul8Q4PGQMWam@google.com/
> - Use TDVMCALL_STATUS prefix for TDX call status codes (Binbin)
> ---
> Documentation/virt/kvm/api.rst | 8 ++++++
> arch/x86/kvm/vmx/tdx.c | 50 ++++++++++++++++++++++++++++++++++
> include/uapi/linux/kvm.h | 1 +
> 3 files changed, 59 insertions(+)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index edc070c6e19b..bb39da72c647 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -6815,6 +6815,7 @@ should put the acknowledged interrupt vector into the 'epr' field.
> #define KVM_SYSTEM_EVENT_WAKEUP 4
> #define KVM_SYSTEM_EVENT_SUSPEND 5
> #define KVM_SYSTEM_EVENT_SEV_TERM 6
> + #define KVM_SYSTEM_EVENT_TDX_FATAL 7
> __u32 type;
> __u32 ndata;
> __u64 data[16];
> @@ -6841,6 +6842,13 @@ Valid values for 'type' are:
> reset/shutdown of the VM.
> - KVM_SYSTEM_EVENT_SEV_TERM -- an AMD SEV guest requested termination.
> The guest physical address of the guest's GHCB is stored in `data[0]`.
> + - KVM_SYSTEM_EVENT_TDX_FATAL -- an TDX guest requested termination.
> + The error codes of the guest's GHCI is stored in `data[0]`.
> + If the bit 63 of `data[0]` is set, it indicates there is TD specified
> + additional information provided in a page, which is shared memory. The
> + guest physical address of the information page is stored in `data[1]`.
> + An optional error message is provided by `data[2]` ~ `data[9]`, which is
> + byte sequence, LSB filled first. Typically, ASCII code(0x20-0x7e) is filled.
> - KVM_SYSTEM_EVENT_WAKEUP -- the exiting vCPU is in a suspended state and
> KVM has recognized a wakeup event. Userspace may honor this event by
> marking the exiting vCPU as runnable, or deny it and call KVM_RUN again.
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 553f4cbe0693..a79f9ca962d1 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -1093,6 +1093,54 @@ static int tdx_map_gpa(struct kvm_vcpu *vcpu)
> return 1;
> }
>
> +static int tdx_report_fatal_error(struct kvm_vcpu *vcpu)
> +{
> + u64 reg_mask = kvm_rcx_read(vcpu);
> + u64* opt_regs;
> +
> + /*
> + * Skip sanity checks and let userspace decide what to do if sanity
> + * checks fail.
> + */
> + vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT;
> + vcpu->run->system_event.type = KVM_SYSTEM_EVENT_TDX_FATAL;
> + vcpu->run->system_event.ndata = 10;
> + /* Error codes. */
> + vcpu->run->system_event.data[0] = tdvmcall_a0_read(vcpu);
> + /* GPA of additional information page. */
> + vcpu->run->system_event.data[1] = tdvmcall_a1_read(vcpu);
> + /* Information passed via registers (up to 64 bytes). */
> + opt_regs = &vcpu->run->system_event.data[2];
> +
> +#define COPY_REG(REG, MASK) \
> + do { \
> + if (reg_mask & MASK) \
> + *opt_regs = kvm_ ## REG ## _read(vcpu); \
> + else \
> + *opt_regs = 0; \
> + opt_regs++; \

I'm not sure if we need to skip the "opt_regs++" the corresponding
register is not set valid in reg_mask. And maintain ndata to actual
valid number instead of hardcoding it to 10.

> + } while (0)
> +
> + /* The order is defined in GHCI. */
> + COPY_REG(r14, BIT_ULL(14));
> + COPY_REG(r15, BIT_ULL(15));
> + COPY_REG(rbx, BIT_ULL(3));
> + COPY_REG(rdi, BIT_ULL(7));
> + COPY_REG(rsi, BIT_ULL(6));
> + COPY_REG(r8, BIT_ULL(8));
> + COPY_REG(r9, BIT_ULL(9));
> + COPY_REG(rdx, BIT_ULL(2));
> +
> + /*
> + * Set the status code according to GHCI spec, although the vCPU may
> + * not return back to guest.
> + */
> + tdvmcall_set_return_code(vcpu, TDVMCALL_STATUS_SUCCESS);
> +
> + /* Forward request to userspace. */
> + return 0;
> +}
> +
> static int handle_tdvmcall(struct kvm_vcpu *vcpu)
> {
> if (tdvmcall_exit_type(vcpu))
> @@ -1101,6 +1149,8 @@ static int handle_tdvmcall(struct kvm_vcpu *vcpu)
> switch (tdvmcall_leaf(vcpu)) {
> case TDVMCALL_MAP_GPA:
> return tdx_map_gpa(vcpu);
> + case TDVMCALL_REPORT_FATAL_ERROR:
> + return tdx_report_fatal_error(vcpu);
> default:
> break;
> }
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 637efc055145..c173c8dfcf83 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -375,6 +375,7 @@ struct kvm_run {
> #define KVM_SYSTEM_EVENT_WAKEUP 4
> #define KVM_SYSTEM_EVENT_SUSPEND 5
> #define KVM_SYSTEM_EVENT_SEV_TERM 6
> +#define KVM_SYSTEM_EVENT_TDX_FATAL 7
> __u32 type;
> __u32 ndata;
> union {