linux-kernel - Re: [PATCH 1/2] x86/mm: Allow guest.enc_status_change

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Message-ID: <20230526114905.ios6la7foypydsbe@box.shutemov.name>
Date:   Fri, 26 May 2023 14:49:05 +0300
From:   "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
To:     "Huang, Kai" <kai.huang@...el.com>
Cc:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "bp@...en8.de" <bp@...en8.de>, "Cui, Dexuan" <decui@...rosoft.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH 1/2] x86/mm: Allow guest.enc_status_change_prepare() to
 fail

On Fri, May 26, 2023 at 02:17:12AM +0000, Huang, Kai wrote:
> On Fri, 2023-05-26 at 01:58 +0300, Kirill A. Shutemov wrote:
> > TDX code is going to provide guest.enc_status_change_prepare() that is
> > able to fail.
> > 
> > Add a way to return an error from the callback.
> > 
> > While there, fix enc_status_change_finish_noop(). It is defined as
> > always-fail now which doesn't make sense for noop.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > Cc: stable@...r.kernel.org
> > ---
> >  arch/x86/include/asm/x86_init.h | 2 +-
> >  arch/x86/kernel/x86_init.c      | 4 ++--
> >  arch/x86/mm/mem_encrypt_amd.c   | 4 +++-
> >  arch/x86/mm/pat/set_memory.c    | 3 ++-
> >  4 files changed, 8 insertions(+), 5 deletions(-)
> > 
> > diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
> > index 88085f369ff6..1ca9701917c5 100644
> > --- a/arch/x86/include/asm/x86_init.h
> > +++ b/arch/x86/include/asm/x86_init.h
> > @@ -150,7 +150,7 @@ struct x86_init_acpi {
> >   * @enc_cache_flush_required	Returns true if a cache flush is needed before changing page encryption status
> >   */
> >  struct x86_guest {
> > -	void (*enc_status_change_prepare)(unsigned long vaddr, int npages, bool enc);
> > +	bool (*enc_status_change_prepare)(unsigned long vaddr, int npages, bool enc);
> > 
> 
> [...]
> 
> > @@ -2151,7 +2151,8 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
> >  		cpa_flush(&cpa, x86_platform.guest.enc_cache_flush_required());
> >  
> >  	/* Notify hypervisor that we are about to set/clr encryption attribute. */
> > -	x86_platform.guest.enc_status_change_prepare(addr, numpages, enc);
> > +	if (!x86_platform.guest.enc_status_change_prepare(addr, numpages, enc))
> > +		return -EIO;
> 
> The name "enc_status_change_prepare()" sounds like an action, but not some
> true/false condition check.  I think it's more reasonable to make it return
> 'int', and returning 0 means successful?

It copies convention of enc_status_change_finish(). I don't think we need
anything more than binary pass/fail. We can change it in the future if
needed.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov