linux-kernel - Re: [PATCH v9 0/5] arm64: ptdump: View the second stage page-tables

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Message-ID: <8634mmvyx0.wl-maz@kernel.org>
Date: Fri, 30 Aug 2024 16:00:11 +0100
From: Marc Zyngier <maz@...nel.org>
To: Sebastian Ene <sebastianene@...gle.com>
Cc: akpm@...ux-foundation.org,
	alexghiti@...osinc.com,
	ankita@...dia.com,
	ardb@...nel.org,
	catalin.marinas@....com,
	christophe.leroy@...roup.eu,
	james.morse@....com,
	vdonnefort@...gle.com,
	mark.rutland@....com,
	oliver.upton@...ux.dev,
	rananta@...gle.com,
	ryan.roberts@....com,
	shahuang@...hat.com,
	suzuki.poulose@....com,
	will@...nel.org,
	yuzenghui@...wei.com,
	kvmarm@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	kernel-team@...roid.com
Subject: Re: [PATCH v9 0/5] arm64: ptdump: View the second stage page-tables

On Fri, 30 Aug 2024 15:44:39 +0100,
Marc Zyngier <maz@...nel.org> wrote:
> 
> Hi Seb,

[...]

> I've been giving this a go on my test systems with 16k pages, and it
> doesn't really work as advertised:
> 
> root@...ette:/sys/kernel/debug/kvm# cat 2573-13/stage2_*
> 2
> ---[ Guest IPA ]---
> 0x0000000000000000-0x0000000008000000         128M 
> 0x0000000008000000-0x00000000090a0000       17024K 3
> 0x00000000090a0000-0x00000000090a4000          16K 3   R W X AF    
> 0x00000000090a4000-0x000000000a000000       15728K 3
> 
> Only 16kB mapped? This is a full Linux guest running the Debian
> installer, and just the kernel is about 20MB (the VM has 4GB of RAM,
> and is using QEMU as the VMM)
> 
> So clearly something isn't playing as expected. Also, this '128M'
> without a level being displayed makes me wonder. It is probably the
> QEMU flash, but then the rest of the addresses don't make much sense
> (RAM on QEMU is at 1GB, not at 128MB.
> 
> On another system with kvmtool, I get something similar:
> 
> root@...denum:/home/maz# cat /sys/kernel/debug/kvm/*/stage2_*
> 2
> ---[ Guest IPA ]---
> 0x0000000000000000-0x0000000001020000       16512K 3
> 0x0000000001020000-0x0000000001024000          16K 3   R W X AF    
> 0x0000000001024000-0x0000000002000000       16240K 3
> 
> and kvmtool places the RAM at 2GB. Clearly not what we're seeing here.
> 
> Could you please verify this?

For the record, on a 4kB host, I get much more plausible results:

root@...-leg-emma:/home/maz# cat /sys/kernel/debug/kvm/632-12/stage2_*
3
---[ Guest IPA ]---
0x0000000000000000-0x0000000000200000           2M 2   R     AF BLK
0x0000000000200000-0x0000000040000000        1022M 2
0x0000000040000000-0x0000000040200000           2M 2   R W X AF BLK
0x0000000040200000-0x0000000044000000          62M 2
0x0000000044000000-0x0000000044200000           2M 2   R W X AF BLK
0x0000000044200000-0x0000000047600000          52M 2
0x0000000047600000-0x0000000047800000           2M 2   R W   AF BLK
0x0000000047800000-0x0000000047e00000           6M 2   R W X AF BLK
0x0000000047e00000-0x0000000048000000           2M 2   R W   AF BLK
0x0000000048000000-0x00000000b9c00000        1820M 2
0x00000000b9c00000-0x00000000b9e00000           2M 2   R W X AF BLK
0x00000000b9e00000-0x00000000bb800000          26M 2
0x00000000bb800000-0x00000000bba00000           2M 2   R W X AF BLK
0x00000000bba00000-0x00000000bbe00000           4M 2   R W   AF BLK
0x00000000bbe00000-0x00000000bc200000           4M 2   R W X AF BLK
0x00000000bc200000-0x00000000bc800000           6M 2   R W   AF BLK
0x00000000bc800000-0x00000000be400000          28M 2
0x00000000be400000-0x00000000bf800000          20M 2   R W X AF BLK
0x00000000bf800000-0x00000000bfe00000           6M 2   R W   AF BLK
0x00000000bfe00000-0x00000000c0000000           2M 2   R W X AF BLK

So 16kB is the one that needs investigating, and I strongly suspect
that 64kB is in the same boat...

Thanks,

	M. (signing off for the day)

-- 
Without deviation from the norm, progress is not possible.