Date:   Thu, 16 Dec 2021 02:37:06 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To:     Josh Poimboeuf <jpoimboe@redhat.com>
Cc:     tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@intel.com, luto@kernel.org, peterz@infradead.org,
        sathyanarayanan.kuppuswamy@linux.intel.com, aarcange@redhat.com,
        ak@linux.intel.com, dan.j.williams@intel.com, david@redhat.com,
        hpa@zytor.com, jgross@suse.com, jmattson@google.com,
        joro@8bytes.org, knsathya@kernel.org, pbonzini@redhat.com,
        sdeep@vmware.com, seanjc@google.com, tony.luck@intel.com,
        vkuznets@redhat.com, wanpengli@tencent.com, x86@kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 08/26] x86/tdx: Handle in-kernel MMIO
Message-ID: <20211215233706.6zjqfvpbcx3omszp@black.fi.intel.com>
References: <20211214150304.62613-1-kirill.shutemov@linux.intel.com>
 <20211214150304.62613-9-kirill.shutemov@linux.intel.com>
 <20211215233116.d2opfoei42viqdty@treble>
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On Wed, Dec 15, 2021 at 03:31:16PM -0800, Josh Poimboeuf wrote:
> On Tue, Dec 14, 2021 at 06:02:46PM +0300, Kirill A. Shutemov wrote:
> > @@ -155,6 +157,108 @@ static bool tdx_handle_cpuid(struct pt_regs *regs)
> >  	return true;
> >  }
> >  
> > +static bool tdx_mmio(int size, bool write, unsigned long addr,
> > +		     unsigned long *val)
> > +{
> > +	struct tdx_hypercall_output out;
> > +	u64 err;
> > +
> > +	err = _tdx_hypercall(EXIT_REASON_EPT_VIOLATION, size, write,
> > +			     addr, *val, &out);
> > +	if (err)
> > +		return true;
> > +
> > +	*val = out.r11;
> > +	return false;
> > +}
> > +
> > +static bool tdx_mmio_read(int size, unsigned long addr, unsigned long *val)
> > +{
> > +	return tdx_mmio(size, false, addr, val);
> > +}
> > +
> > +static bool tdx_mmio_write(int size, unsigned long addr, unsigned long *val)
> > +{
> > +	return tdx_mmio(size, true, addr, val);
> > +}
> 
> These bool functions return false on success.  Conversely, other
> functions in this file return true on success.  That inconsistency is
> really confusing for the callers and is bound to introduce bugs
> eventually.
> 
> > +static int tdx_handle_mmio(struct pt_regs *regs, struct ve_info *ve)
> 
> Similarly, tdx_handle_mmio() returns (int) 0 for success, while other
> tdx_handle_*() functions return (bool) true for success.  Also
> confusing.
> 
> The most robust option would be for all the functions to follow the
> typical kernel convention of returning (int) 0 on success.  It works for
> 99.99% of the kernel.  Why mess with success? (pun intended)
> 
> Otherwise it's just pointless added cognitive overhead, trying to keep
> track of what success means, for each individual function.

Okay, fair enough. I will make them consistent.

-- 
 Kirill A. Shutemov