[PATCH V2 01/12] x86/virt/tdx: Make tdh_vp_enter() noinstr

Adrian Hunter
2025-01-29T09:59:45Z

Make tdh_vp_enter() noinstr because KVM requires VM entry to be noinstr
for 2 reasons:
1. The use of context tracking via guest_state_enter_irqoff() and
guest_state_exit_irqoff()
2. The need to avoid IRET between VM-exit and NMI handling in order to
avoid prematurely releasing NMI inhibit.

Consequently make __seamcall_saved_ret() noinstr also. Currently
tdh_vp_enter() is the only caller of __seamcall_saved_ret().

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
TD vcpu enter/exit v2:
- New patch
---
arch/x86/virt/vmx/tdx/seamcall.S | 3 +++
arch/x86/virt/vmx/tdx/tdx.c | 2 +-
2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/virt/vmx/tdx/seamcall.S b/arch/x86/virt/vmx/tdx/seamcall.S
index 5b1f2286aea9..6854c52c374b 100644
--- a/arch/x86/virt/vmx/tdx/seamcall.S
+++ b/arch/x86/virt/vmx/tdx/seamcall.S
@@ -41,6 +41,9 @@ SYM_FUNC_START(__seamcall_ret)
TDX_MODULE_CALL host=1 ret=1
SYM_FUNC_END(__seamcall_ret)

+/* KVM requires non-instrumentable __seamcall_saved_ret() for TDH.VP.ENTER */
+.section .noinstr.text, "ax"
+
/*
* __seamcall_saved_ret() - Host-side interface functions to SEAM software
* (the P-SEAMLDR or the TDX module), with saving output registers to the
diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index 4a010e65276d..1515c467dd86 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -1511,7 +1511,7 @@ static void tdx_clflush_page(struct page *page)
clflush_cache_range(page_to_virt(page), PAGE_SIZE);
}

-u64 tdh_vp_enter(struct tdx_vp *td, struct tdx_module_args *args)
+noinstr u64 tdh_vp_enter(struct tdx_vp *td, struct tdx_module_args *args)
{
args->rcx = tdx_tdvpr_pa(td);

--
2.43.0