linux-kernel - Re: [RESEND PATCH v5] arm64: Enable vmalloc-huge with ptdump

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Message-ID: <b93b0cca-04ac-402c-b522-cda8f39a52bc@arm.com>
Date: Fri, 19 Sep 2025 17:44:52 +0530
From: Dev Jain <dev.jain@....com>
To: Will Deacon <will@...nel.org>
Cc: catalin.marinas@....com, anshuman.khandual@....com,
 quic_zhenhuah@...cinc.com, ryan.roberts@....com, kevin.brodsky@....com,
 yangyicong@...ilicon.com, joey.gouly@....com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 david@...hat.com, mark.rutland@....com, urezki@...il.com,
 jthoughton@...gle.com
Subject: Re: [RESEND PATCH v5] arm64: Enable vmalloc-huge with ptdump


On 19/09/25 4:29 pm, Will Deacon wrote:
> On Fri, Sep 19, 2025 at 03:58:46PM +0530, Dev Jain wrote:
>> On 17/09/25 9:13 pm, Will Deacon wrote:
>>> On Tue, Sep 16, 2025 at 11:30:26AM +0100, Will Deacon wrote:
>>>> I'm currently trying to put together a litmus test with James (cc'd) so
>>>> maybe we can help you out with that part.
>>> Here's what we came up with. There's not a good way to express the IPI
>>> from kick_all_cpus_sync() but it turns out that the ISB from the TLB
>>> invalidation is sufficient anyway. Does it make sense to you?
>>>
>>>
>>> AArch64 ptdump
>>> Variant=Ifetch
>>> {
>>> uint64_t pud=0xa110c;
>>> uint64_t pmd;
>>>
>>> 0:X0=label:"P1:L0"; 0:X1=instr:"NOP"; 0:X2=lock; 0:X3=pud; 0:X4=pmd;
>>>                       1:X1=0xdead;      1:X2=lock; 1:X3=pud; 1:X4=pmd;
>>> }
>>>    P0				| P1				;
>>>    (* static_key_enable *)	| (* pud_free_pmd_page *)	;
>>>    STR	W1, [X0]		| LDR	X9, [X3]		;
>>>    DC	CVAU,X0			| STR	XZR, [X3]		;
>>>    DSB	ISH			| DSB	ISH			;
>>>    IC	IVAU,X0			| ISB				;
>>>    DSB	ISH			|				;
>>>    ISB				| (* static key *)		;
>>> 				| L0:				;
>>>    (* mmap_lock *)		| B	out1			;
>>>    Lwlock:			|				;
>>>    MOV	W7, #1			| (* mmap_lock *)		;
>>>    SWPA	W7, W8, [X2]		| Lrlock:			;
>>> 				| MOV	W7, #1			;
>>> 				| SWPA	W7, W8, [X2]		;
>>>    (* walk pgtable *)		|				;
>>>    LDR	X9, [X3]		| (* mmap_unlock *)		;
>>>    CBZ	X9, out0		| STLR	WZR, [X2]		;
>>>    EOR	X10, X9, X9		|				;
>>>    LDR	X11, [X4, X10]		| out1:				;
>>> 				| EOR	X10, X9, X9		;
>>>    out0:				| STR	X1, [X4, X10]		;
>>>
>>> exists (0:X8=0 /\ 1:X8=0 /\	(* Lock acquisitions succeed *)
>>> 	0:X9=0xa110c /\		(* P0 sees the valid PUD ...*)
>>> 	0:X11=0xdead)		(* ... but the freed PMD *)
>>>
>>>
>>> Will
>> Is the syntax correct? I cannot use the herd7 command to run this.
> Weird, what happens? It runs for me:
>
> $ herd7 -version
> 7.58+1, Rev: e39a86f5d59dee3174d08d9ab5b13155c75936fd
>
> $ herd7 ptdump.litmus
> Test ptdump Allowed
> States 5
> 0:X8=0; 0:X9=0; 0:X11=0; 1:X8=0;
> 0:X8=0; 0:X9=0; 0:X11=0; 1:X8=1;
> 0:X8=0; 0:X9=659724; 0:X11=0; 1:X8=1;
> 0:X8=0; 0:X9=659724; 0:X11=57005; 1:X8=1;
> 0:X8=1; 0:X9=0; 0:X11=0; 1:X8=0;
> No
> Witnesses
> Positive: 0 Negative: 9
> Flag Assuming-common-inner-shareable-domain
> Condition exists (0:X8=0 /\ 1:X8=0 /\ 0:X9=659724 /\ 0:X11=57005)
> Observation ptdump Never 0 9
> Time ptdump 1.65
> Hash=238908ee9413a36507c61b92a31a366a

I was using some other command :) yup this works.

I'll try posting the next version today itself, but will you be
okay merging this if I post on Monday?

>
> Will