On Fri, Oct 24, 2025, Kai Huang wrote:

On Thu, 2025-10-16 at 17:32 -0700, Sean Christopherson wrote:

quoted

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@google.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()?

+1, definitely needs a comment.

/*
 * Execute a SEAMCALL related to removing/blocking S-EPT entries, with a single
 * retry (if necessary) after forcing vCPUs to exit and wait for the operation
 * to complete.  All flows that remove/block S-EPT entries run with mmu_lock
 * held for write, i.e. are mutually exlusive with each other, but they aren't
 * mutually exclusive with vCPUs running (because that would be overkill), and
 * so can fail with "operand busy" if a vCPU acquires a required lock in the
 * TDX-Module.
 *
 * Note, the retry is guaranteed to succeed, absent KVM and/or TDX-Module bugs.
 */
 

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

Heh, this also caught my eye when typing up the comment.  Unfortunately, I don't
think it's worth doing the TDX_BUG_ON() inside the macro as that would require
plumbing in the UPPERCASE name, and doesn't work well with the variadic arguments,
e.g. TRACK wants TDX_BUG_ON(), but REMOVE and BLOCK want TDX_BUG_ON_2().

Given that REMOVE and BLOCK need to check the return value, getting the TDX_BUG_ON()
call into the macro wouldn't buy that much.