From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
luto@kernel.org, peterz@infradead.org, ak@linux.intel.com,
dan.j.williams@intel.com, david@redhat.com, hpa@zytor.com,
linux-kernel@vger.kernel.org,
sathyanarayanan.kuppuswamy@linux.intel.com, seanjc@google.com,
thomas.lendacky@amd.com, x86@kernel.org
Subject: Re: [PATCHv4 3/3] x86/tdx: Handle load_unaligned_zeropad() page-cross to a shared page
Date: Thu, 16 Jun 2022 04:19:26 +0300 [thread overview]
Message-ID: <20220616011926.hjmogvbzo6e4d5cj@black.fi.intel.com> (raw)
In-Reply-To: <db63853f-dbd8-7593-032d-e674046bff8e@intel.com>
On Wed, Jun 15, 2022 at 04:34:48PM -0700, Dave Hansen wrote:
> 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 it fixes anything.
Consider the case when vaddr is 4092 and size is 4. This is legitimate
access -- aligned and not page crosser.
The left side of the check will be evaluated to 0 and the right will be 1
which is wrong and will get us -EFAULT.
I cannot think of a helper that would fit the need.
--
Kirill A. Shutemov
next prev parent reply other threads:[~2022-06-16 1:19 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-14 12:01 [PATCHv4 0/3] An updated version of the load_unaligned_zeropad() fix Kirill A. Shutemov
2022-06-14 12:01 ` [PATCHv4 1/3] x86/tdx: Fix early #VE handling Kirill A. Shutemov
2022-06-17 21:53 ` [tip: x86/urgent] " tip-bot2 for Kirill A. Shutemov
2022-06-14 12:01 ` [PATCHv4 2/3] x86/tdx: Clarify RIP adjustments in #VE handler Kirill A. Shutemov
2022-06-17 21:53 ` [tip: x86/urgent] " tip-bot2 for Kirill A. Shutemov
2022-06-14 12:01 ` [PATCHv4 3/3] x86/tdx: Handle load_unaligned_zeropad() page-cross to a shared page Kirill A. Shutemov
2022-06-15 15:27 ` Dave Hansen
2022-06-15 17:10 ` Kirill A. Shutemov
2022-06-15 21:55 ` Dave Hansen
2022-06-15 22:43 ` Kirill A. Shutemov
2022-06-15 22:49 ` Dave Hansen
2022-06-15 23:16 ` Kirill A. Shutemov
2022-06-15 18:12 ` Dave Hansen
2022-06-15 22:32 ` Kirill A. Shutemov
2022-06-15 22:36 ` Dave Hansen
2022-06-15 23:16 ` Kirill A. Shutemov
2022-06-15 22:52 ` Kirill A. Shutemov
2022-06-15 23:34 ` Dave Hansen
2022-06-16 1:19 ` Kirill A. Shutemov [this message]
2022-06-16 6:35 ` David Laight
2022-06-17 21:53 ` [tip: x86/urgent] " tip-bot2 for Kirill A. Shutemov
2022-06-17 22:41 ` tip-bot2 for Kirill A. Shutemov
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