linux-kernel - Re: [PATCH v5 09/10] KVM: SVM: Use new ccp GCTX API

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Message-ID: <ZzTubiWtfmNTPlLK@google.com>
Date: Wed, 13 Nov 2024 10:22:38 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Tom Lendacky <thomas.lendacky@....com>
Cc: Dionna Amalie Glaze <dionnaglaze@...gle.com>, linux-kernel@...r.kernel.org, x86@...nel.org, 
	Paolo Bonzini <pbonzini@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	"H. Peter Anvin" <hpa@...or.com>, linux-coco@...ts.linux.dev, 
	Ashish Kalra <ashish.kalra@....com>, John Allen <john.allen@....com>, 
	Herbert Xu <herbert@...dor.apana.org.au>, "David S. Miller" <davem@...emloft.net>, 
	Michael Roth <michael.roth@....com>, Luis Chamberlain <mcgrof@...nel.org>, 
	Russ Weight <russ.weight@...ux.dev>, Danilo Krummrich <dakr@...hat.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Tianfei zhang <tianfei.zhang@...el.com>, Alexey Kardashevskiy <aik@....com>, kvm@...r.kernel.org
Subject: Re: [PATCH v5 09/10] KVM: SVM: Use new ccp GCTX API

On Tue, Nov 12, 2024, Tom Lendacky wrote:
> On 11/12/24 13:33, Dionna Amalie Glaze wrote:
> >>> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> >>> index cea41b8cdabe4..d7cef84750b33 100644
> >>> --- a/arch/x86/kvm/svm/sev.c
> >>> +++ b/arch/x86/kvm/svm/sev.c
> >>> @@ -89,7 +89,7 @@ static unsigned int nr_asids;
> >>>  static unsigned long *sev_asid_bitmap;
> >>>  static unsigned long *sev_reclaim_asid_bitmap;
> >>>
> >>> -static int snp_decommission_context(struct kvm *kvm);
> >>> +static int kvm_decommission_snp_context(struct kvm *kvm);
> >>
> >> Why the name change? It seems like it just makes the patch a bit harder
> >> to follow since there are two things going on.
> >>
> > 
> > KVM and ccp both seem to like to name their functions starting with
> > sev_ or snp_, and it's particularly hard to determine provenance.
> > 
> > snp_decommision_context and sev_snp_guest_decommission... which is
> > from where? It's weird to me.
> 
> I guess I don't see the problem, a quick git grep -w of the name will
> show you where each is. Its a static function in the file, so if
> anything just changing/shortening the name to decommission_snp_context()

Eh, that creates just as many problems as it solves, because it mucks up the
namespace and leads to discontinuity between the decommission helper and things
like snp_launch_update_vmsa() and snp_launch_finish().

I agree that there isn't a strong need to fixup static symbols.  That said, I do
think drivers/crypto/ccp/sev-dev.c in particular needs a different namespace, and
needs to use it consistently, to make it somewhat obvious that it's (almost) all
about the PSP/ASP.

But IMO, an even bigger mess in that area is the lack of consistency in the APIs
themselves.  E.g. this code where KVM uses sev_do_cmd() directly for SNP, but
bounces through a wrapper for !SNP.  Eww.

	wbinvd_on_all_cpus();

	if (sev_snp_enabled)
		ret = sev_do_cmd(SEV_CMD_SNP_DF_FLUSH, NULL, &error);
	else
		ret = sev_guest_df_flush(&error);

	up_write(&sev_deactivate_lock);


And then KVM has snp_page_reclaim(), but the PSP/ASP driver has snp_reclaim_pages().

So if we want to start renaming things, I vote to go a step further and clean up
the APIs, e.g. with a goal of eliminating sev_do_cmd(), and possibly of making
the majority of the PSP-defined structures in include/linux/psp-sev.h "private"
to the PSP/ASP driver.

> would be better (especially since nothing in the svm directory should
> have a name that starts with kvm_).

+1 to not using "kvm_".  KVM often uses "kvm_" to differentiate globally visible
symbols from local (static) symbols.  I.e. prepending "kvm_" just trades one
confusing name for another.