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From: Pavel Tatashin <pasha.tatashin@soleen.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Tyler Hicks <tyhicks@linux.microsoft.com>,
	James Morris <jmorris@namei.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Mike Rapoport <rppt@kernel.org>,
	Logan Gunthorpe <logang@deltatee.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 1/1] arm64: mm: correct the inside linear map boundaries during hotplug check
Date: Mon, 15 Feb 2021 17:28:18 -0500	[thread overview]
Message-ID: <CA+CK2bDX9X+SdHOB=dd2kvsYfQwPvhuVNRByZW8sENuzuHRZyQ@mail.gmail.com> (raw)
In-Reply-To: <CA+CK2bDJ7Y2-vEpZrZ0fzigAfDgcJOmjhmin_GjTqioYXAYB3Q@mail.gmail.com>

> >
> > Btw, the KASLR check is incorrect: memstart_addr could also be
> > negative when running the 52-bit VA kernel on hardware that is only
> > 48-bit VA capable.
>
> Good point!
>
> if (IS_ENABLED(CONFIG_ARM64_VA_BITS_52) && (vabits_actual != 52))
>     memstart_addr -= _PAGE_OFFSET(48) - _PAGE_OFFSET(52);
>
> So, I will remove IS_ENABLED(CONFIG_RANDOMIZE_BASE) again.

Hi Ard,

Actually, looking more at this, I do not see how with 52VA on a 48VA
processor start offset can become negative unless randomization is
involved.
The start of the linear map will point to the first physical address
that is reported by memblock_start_of_DRAM(). However, memstart_addr
will be negative. So, I think the current approach using
IS_ENABLED(CONFIG_RANDOMIZE_BASE) is good.

48VA processor with VA_BITS_48:
memstart_addr 40000000
start_linear_pa 40000000
end_linear_pa 80003fffffff

48VA processor with VA_BITS_52:
memstart_addr fff1000040000000   <- Negative
start_linear_pa 40000000  <- positive, and the first PA address
end_linear_pa 80003fffffff

Thank you,
Pasha

WARNING: multiple messages have this Message-ID (diff)
From: Pavel Tatashin <pasha.tatashin@soleen.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	James Morris <jmorris@namei.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Logan Gunthorpe <logang@deltatee.com>,
	Tyler Hicks <tyhicks@linux.microsoft.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Will Deacon <will@kernel.org>, Mike Rapoport <rppt@kernel.org>
Subject: Re: [PATCH v2 1/1] arm64: mm: correct the inside linear map boundaries during hotplug check
Date: Mon, 15 Feb 2021 17:28:18 -0500	[thread overview]
Message-ID: <CA+CK2bDX9X+SdHOB=dd2kvsYfQwPvhuVNRByZW8sENuzuHRZyQ@mail.gmail.com> (raw)
In-Reply-To: <CA+CK2bDJ7Y2-vEpZrZ0fzigAfDgcJOmjhmin_GjTqioYXAYB3Q@mail.gmail.com>

> >
> > Btw, the KASLR check is incorrect: memstart_addr could also be
> > negative when running the 52-bit VA kernel on hardware that is only
> > 48-bit VA capable.
>
> Good point!
>
> if (IS_ENABLED(CONFIG_ARM64_VA_BITS_52) && (vabits_actual != 52))
>     memstart_addr -= _PAGE_OFFSET(48) - _PAGE_OFFSET(52);
>
> So, I will remove IS_ENABLED(CONFIG_RANDOMIZE_BASE) again.

Hi Ard,

Actually, looking more at this, I do not see how with 52VA on a 48VA
processor start offset can become negative unless randomization is
involved.
The start of the linear map will point to the first physical address
that is reported by memblock_start_of_DRAM(). However, memstart_addr
will be negative. So, I think the current approach using
IS_ENABLED(CONFIG_RANDOMIZE_BASE) is good.

48VA processor with VA_BITS_48:
memstart_addr 40000000
start_linear_pa 40000000
end_linear_pa 80003fffffff

48VA processor with VA_BITS_52:
memstart_addr fff1000040000000   <- Negative
start_linear_pa 40000000  <- positive, and the first PA address
end_linear_pa 80003fffffff

Thank you,
Pasha

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2021-02-15 22:31 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-15 19:22 [PATCH v2 0/1] correct the inside linear map boundaries during hotplug check Pavel Tatashin
2021-02-15 19:22 ` Pavel Tatashin
2021-02-15 19:22 ` [PATCH v2 1/1] arm64: mm: " Pavel Tatashin
2021-02-15 19:22   ` Pavel Tatashin
2021-02-15 19:27   ` Ard Biesheuvel
2021-02-15 19:27     ` Ard Biesheuvel
2021-02-15 19:30     ` Pavel Tatashin
2021-02-15 19:30       ` Pavel Tatashin
2021-02-15 19:34       ` Ard Biesheuvel
2021-02-15 19:34         ` Ard Biesheuvel
2021-02-15 19:51         ` Pavel Tatashin
2021-02-15 19:51           ` Pavel Tatashin
2021-02-15 22:28           ` Pavel Tatashin [this message]
2021-02-15 22:28             ` Pavel Tatashin
2021-02-16  3:12           ` Anshuman Khandual
2021-02-16  3:12             ` Anshuman Khandual
2021-02-16  7:36             ` Ard Biesheuvel
2021-02-16  7:36               ` Ard Biesheuvel
2021-02-16 14:34               ` Pavel Tatashin
2021-02-16 14:34                 ` Pavel Tatashin
2021-02-16  2:55     ` Anshuman Khandual
2021-02-16  2:55       ` Anshuman Khandual
2021-02-16 14:48       ` Pavel Tatashin
2021-02-16 14:48         ` Pavel Tatashin

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