linux-kernel - RE: [PATCHv4 3/3] x86/tdx: Handle load_unaligned

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Date:   Thu, 16 Jun 2022 06:35:44 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Dave Hansen' <dave.hansen@...el.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "luto@...nel.org" <luto@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>
CC:     "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "david@...hat.com" <david@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "x86@...nel.org" <x86@...nel.org>
Subject: RE: [PATCHv4 3/3] x86/tdx: Handle load_unaligned_zeropad() page-cross
 to a shared page

From: Dave Hansen
> Sent: 16 June 2022 00:35
> 
> On 6/15/22 15:52, Kirill A. Shutemov wrote:
> >> +	vaddr = (unsigned long)insn_get_addr_ref(&insn, regs);
> >> +	if (vaddr / PAGE_SIZE != (vaddr + size) / PAGE_SIZE)
> > Oops. I just realized it has off-by-one. It supposed to be:
> >
> > 	if (vaddr / PAGE_SIZE != (vaddr + size - 1) / PAGE_SIZE)
> 
> That was bugging me.  Glad you caught this.
> 
> Wouldn't this be more obviously correct?
> 
> 	if (ALIGN_DOWN(vaddr,        PAGE_SIZE) !=
> 	    ALIGN_DOWN(vaddr + size, PAGE_SIZE))
> 		...
> 
> I don't think we have a PAGE_ALIGN_DOWN().

Or:
	if ((vaddr ^ (vaddr + size - 1)) >> PAGE_SHIFT)

	David

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