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

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Message-ID: <0c2bb665-93ee-4f46-ac28-5dbd1dd2b9a2@redhat.com>
Date: Sun, 16 Feb 2025 19:26:34 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Adrian Hunter <adrian.hunter@...el.com>, seanjc@...gle.com
Cc: kvm@...r.kernel.org, rick.p.edgecombe@...el.com, kai.huang@...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: Re: [PATCH V2 01/12] x86/virt/tdx: Make tdh_vp_enter() noinstr

On 1/29/25 10:58, Adrian Hunter wrote:
> 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>

This can be squashed into "x86/virt/tdx: Add SEAMCALL wrapper to 
enter/exit TDX guest"; I did that in kvm-coco-queue.

Paolo

> ---
> 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);
>