linux-kernel - [PATCH V2 01/12] x86/virt/tdx: Make tdh_vp

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Message-ID: <20250129095902.16391-2-adrian.hunter@intel.com>
Date: Wed, 29 Jan 2025 11:58:50 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: pbonzini@...hat.com,
	seanjc@...gle.com
Cc: kvm@...r.kernel.org,
	rick.p.edgecombe@...el.com,
	kai.huang@...el.com,
	adrian.hunter@...el.com,
	reinette.chatre@...el.com,
	xiaoyao.li@...el.com,
	tony.lindgren@...ux.intel.com,
	binbin.wu@...ux.intel.com,
	dmatlack@...gle.com,
	isaku.yamahata@...el.com,
	nik.borisov@...e.com,
	linux-kernel@...r.kernel.org,
	yan.y.zhao@...el.com,
	chao.gao@...el.com,
	weijiang.yang@...el.com,
	dave.hansen@...ux.intel.com,
	x86@...nel.org
Subject: [PATCH V2 01/12] x86/virt/tdx: Make tdh_vp_enter() noinstr

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@...el.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