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

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Message-ID: <aM1MEF3pANiL3p2Z@willie-the-truck>
Date: Fri, 19 Sep 2025 13:26:56 +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 05:44:52PM +0530, Dev Jain wrote:
> 
> 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 *)
> > > > 
> > > > 
> > > 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.

Nice.

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

On my desk 9am, Monday please!

Joking aside: the sooner, the better but please make sure you've tested
the new static key (inc/dec) stuff as I didn't look particularly deeply
into it.

Will