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

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Message-ID: <aM0yQwt3_8WuxBC2@willie-the-truck>
Date: Fri, 19 Sep 2025 11:59:10 +0100
From: Will Deacon <will@...nel.org>
To: Dev Jain <dev.jain@....com>
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 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

Will