linux-kernel - Re: [PATCH v2] x86/kaslr: Revisit entropy when CONFIG_PCI

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Message-ID: <0b7945c5-d776-4313-a15f-d54cfb27aa32@nvidia.com>
Date: Fri, 7 Feb 2025 12:39:40 +1100
From: Balbir Singh <balbirs@...dia.com>
To: Dave Hansen <dave.hansen@...el.com>, x86@...nel.org
Cc: linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
 apopple@...dia.com, jhubbard@...dia.com, jgg@...dia.com,
 Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski
 <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>,
 Kees Cook <kees@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v2] x86/kaslr: Revisit entropy when CONFIG_PCI_P2PDMA is
 enabled

On 2/7/25 11:27, Dave Hansen wrote:
> On 2/6/25 15:42, Balbir Singh wrote:
>> Fix this by not shrinking the size of direct map when CONFIG_PCI_P2PDMA
>> is enabled. This reduces the total available entropy, but it's
>> better than the current work around of having to disable KASLR
>> completely.
> 
> Is the size of these P2PDMA mappings known up front? Or do you just need
> them to be as large as possible?

The size is not known upfront, it depends on the system configuration.
Yes, we need them to be as large as possible.

Balbir