linux-kernel - Re: [PATCH v3 20/25] KVM: TDX: Add macro to retry SEAMCALLs when forcing vCPUs out of guest

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Message-ID: <4809644b0ba02d0987ac56f4be7c426d0724cdef.camel@intel.com>
Date: Fri, 24 Oct 2025 10:09:25 +0000
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Subject: Re: [PATCH v3 20/25] KVM: TDX: Add macro to retry SEAMCALLs when
 forcing vCPUs out of guest

On Thu, 2025-10-16 at 17:32 -0700, Sean Christopherson wrote:
> Add a macro to handle kicking vCPUs out of the guest and retrying
> SEAMCALLs on -EBUSY instead of providing small helpers to be used by each
> SEAMCALL.  Wrapping the SEAMCALLs in a macro makes it a little harder to
> tease out which SEAMCALL is being made, but significantly reduces the
> amount of copy+paste code and makes it all but impossible to leave an
> elevated wait_for_sept_zap.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/vmx/tdx.c | 72 ++++++++++++++----------------------------
>  1 file changed, 23 insertions(+), 49 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index f6782b0ffa98..2e2dab89c98f 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -294,25 +294,24 @@ static inline void tdx_disassociate_vp(struct kvm_vcpu *vcpu)
>  	vcpu->cpu = -1;
>  }
>  
> -static void tdx_no_vcpus_enter_start(struct kvm *kvm)
> -{
> -	struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> -
> -	lockdep_assert_held_write(&kvm->mmu_lock);
> -
> -	WRITE_ONCE(kvm_tdx->wait_for_sept_zap, true);
> -
> -	kvm_make_all_cpus_request(kvm, KVM_REQ_OUTSIDE_GUEST_MODE);
> -}
> -
> -static void tdx_no_vcpus_enter_stop(struct kvm *kvm)
> -{
> -	struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> -
> -	lockdep_assert_held_write(&kvm->mmu_lock);
> -
> -	WRITE_ONCE(kvm_tdx->wait_for_sept_zap, false);
> -}
> +#define tdh_do_no_vcpus(tdh_func, kvm, args...)					\
> +({										\
> +	struct kvm_tdx *__kvm_tdx = to_kvm_tdx(kvm);				\
> +	u64 __err;								\
> +										\
> +	lockdep_assert_held_write(&kvm->mmu_lock);				\
> +										\
> +	__err = tdh_func(args);							\
> +	if (unlikely(tdx_operand_busy(__err))) {				\
> +		WRITE_ONCE(__kvm_tdx->wait_for_sept_zap, true);			\
> +		kvm_make_all_cpus_request(kvm, KVM_REQ_OUTSIDE_GUEST_MODE);	\
> +										\
> +		__err = tdh_func(args);						\
> +										\
> +		WRITE_ONCE(__kvm_tdx->wait_for_sept_zap, false);		\
> +	}									\
> +	__err;									\
> +})

The comment which says "the second retry should succeed" is lost, could we
add it to tdh_do_no_vcpus()?

Also, perhaps we can just TDX_BUG_ON() inside tdh_do_no_vcpus() when the
second call of tdh_func() fails?