linux-kernel - Re: [PATCH v5 3/7] x86/virt/tdx: Mark memory cache state incoherent when making SEAMCALL

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Message-ID: <3bd5e7ff5756b80766553b5dfc28476aff1d0583.camel@intel.com>
Date: Tue, 12 Aug 2025 00:51:38 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "Hansen, Dave" <dave.hansen@...el.com>, "Huang, Kai"
	<kai.huang@...el.com>, "bp@...en8.de" <bp@...en8.de>, "peterz@...radead.org"
	<peterz@...radead.org>, "hpa@...or.com" <hpa@...or.com>, "mingo@...hat.com"
	<mingo@...hat.com>, "tglx@...utronix.de" <tglx@...utronix.de>,
	"thomas.lendacky@....com" <thomas.lendacky@....com>
CC: "ashish.kalra@....com" <ashish.kalra@....com>, "Gao, Chao"
	<chao.gao@...el.com>, "seanjc@...gle.com" <seanjc@...gle.com>,
	"x86@...nel.org" <x86@...nel.org>, "kas@...nel.org" <kas@...nel.org>,
	"sagis@...gle.com" <sagis@...gle.com>, "Chatre, Reinette"
	<reinette.chatre@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Williams, Dan J" <dan.j.williams@...el.com>,
	"Chen, Farrah" <farrah.chen@...el.com>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "pbonzini@...hat.com" <pbonzini@...hat.com>,
	"dwmw@...zon.co.uk" <dwmw@...zon.co.uk>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "nik.borisov@...e.com" <nik.borisov@...e.com>
Subject: Re: [PATCH v5 3/7] x86/virt/tdx: Mark memory cache state incoherent
 when making SEAMCALL

On Tue, 2025-07-29 at 00:28 +1200, Kai Huang wrote:
> +static __always_inline u64 do_seamcall(sc_func_t func, u64 fn,
> +				       struct tdx_module_args *args)
> +{
> +	lockdep_assert_preemption_disabled();
> +
> +	/*
> +	 * SEAMCALLs are made to the TDX module and can generate dirty
> +	 * cachelines of TDX private memory.  Mark cache state incoherent
> +	 * so that the cache can be flushed during kexec.
> +	 *
> +	 * This needs to be done before actually making the SEAMCALL,
> +	 * because kexec-ing CPU could send NMI to stop remote CPUs,
> +	 * in which case even disabling IRQ won't help here.
> +	 */
> +	this_cpu_write(cache_state_incoherent, true);
> +
> +	return func(fn, args);
> +}
> +


Functionally it looks good now, but I still think the chain of names is not
acceptable:

seamcall()
	sc_retry()
		do_seamcall()
			__seamcall()

sc_retry() is the only one with a hint of what is different about it, but it
randomly uses sc abbreviation instead of seamcall. That is an existing thing.
But the additional one should be named with something about the cache part that
it does, like seamcall_dirty_cache() or something. "do_seamcall()" tells the
reader nothing.