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

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Date:   Wed, 15 Jun 2022 16:34:48 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        luto@...nel.org, peterz@...radead.org
Cc:     ak@...ux.intel.com, dan.j.williams@...el.com, david@...hat.com,
        hpa@...or.com, linux-kernel@...r.kernel.org,
        sathyanarayanan.kuppuswamy@...ux.intel.com, seanjc@...gle.com,
        thomas.lendacky@....com, x86@...nel.org
Subject: Re: [PATCHv4 3/3] x86/tdx: Handle load_unaligned_zeropad() page-cross
 to a shared page

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().