linux-kernel - Re: [RFC][PATCH 05/12] arch: Introduce arch_{,try_}_cmpxchg128{,

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Y7RiDadEzeU3JnaO@osiris>
Date:   Tue, 3 Jan 2023 18:12:45 +0100
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     torvalds@...ux-foundation.org, corbet@....net, will@...nel.org,
        boqun.feng@...il.com, mark.rutland@....com,
        catalin.marinas@....com, dennis@...nel.org, tj@...nel.org,
        cl@...ux.com, gor@...ux.ibm.com, agordeev@...ux.ibm.com,
        borntraeger@...ux.ibm.com, svens@...ux.ibm.com,
        Herbert Xu <herbert@...dor.apana.org.au>, davem@...emloft.net,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        joro@...tes.org, suravee.suthikulpanit@....com,
        robin.murphy@....com, dwmw2@...radead.org,
        baolu.lu@...ux.intel.com, Arnd Bergmann <arnd@...db.de>,
        penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
        Andrew Morton <akpm@...ux-foundation.org>, vbabka@...e.cz,
        roman.gushchin@...ux.dev, 42.hyeyoo@...il.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-s390@...r.kernel.org,
        linux-crypto@...r.kernel.org, iommu@...ts.linux.dev,
        linux-arch@...r.kernel.org
Subject: Re: [RFC][PATCH 05/12] arch: Introduce
 arch_{,try_}_cmpxchg128{,_local}()

On Mon, Dec 19, 2022 at 04:35:30PM +0100, Peter Zijlstra wrote:
> For all architectures that currently support cmpxchg_double()
> implement the cmpxchg128() family of functions that is basically the
> same but with a saner interface.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  arch/arm64/include/asm/atomic_ll_sc.h |   38 +++++++++++++++++++++++
>  arch/arm64/include/asm/atomic_lse.h   |   33 +++++++++++++++++++-
>  arch/arm64/include/asm/cmpxchg.h      |   26 ++++++++++++++++
>  arch/s390/include/asm/cmpxchg.h       |   33 ++++++++++++++++++++
>  arch/x86/include/asm/cmpxchg_32.h     |    3 +
>  arch/x86/include/asm/cmpxchg_64.h     |   55 +++++++++++++++++++++++++++++++++-
>  6 files changed, 185 insertions(+), 3 deletions(-)
...
> --- a/arch/s390/include/asm/cmpxchg.h
> +++ b/arch/s390/include/asm/cmpxchg.h
> @@ -201,4 +201,37 @@ static __always_inline int __cmpxchg_dou
>  			 (unsigned long)(n1), (unsigned long)(n2));	\
>  })
>  
> +#define system_has_cmpxchg128()		1
> +
> +static __always_inline u128 arch_cmpxchg128(volatile u128 *ptr, u128 old, u128 new)
> +{
> +	asm volatile(
> +		"	cdsg	%[old],%[new],%[ptr]\n"
> +		: [old] "+&d" (old)
> +		: [new] "d" (new),
> +		  [ptr] "QS" (*(unsigned long *)ptr)
> +		: "memory", "cc");
> +	return old;
> +}
> +
> +static __always_inline bool arch_try_cmpxchg128(volatile u128 *ptr, u128 *oldp, u128 new)
> +{
> +	u128 old = *oldp;
> +	int cc;
> +
> +	asm volatile(
> +		"	cdsg	%[old],%[new],%[ptr]\n"
> +		"	ipm	%[cc]\n"
> +		"	srl	%[cc],28\n"
> +		: [cc] "=&d" (cc), [old] "+&d" (old)
> +		: [new] "d" (new),
> +		  [ptr] "QS" (*(unsigned long *)ptr)
> +		: "memory", "cc");
> +
> +	if (unlikely(!cc))
> +		*oldp = old;
> +
> +	return likely(cc);
> +}
> +

I was wondering why arch_try_cmpxchg128() isn't even used with later
code. Turned out this is because of a missing

#define arch_try_cmpxchg128 arch_try_cmpxchg128

which in turn means that the generic fallback variant is used.

The above arch_try_cmpxchg128() implementation is broken, since it has
inversed condition code handling (cc == 0 means compare and swap
succeeded, cc == 1 means it failed).

However I would prefer to use the generic fallback variant anyway.
Could you please merge the below into your current patch?

It addresses also the oddity that *ptr within arch_cmpxchg128() is
only specified as input, while it should be input/output - it doesn't
matter due to the memory clobber, but let's have that correct anyway.

diff --git a/arch/s390/include/asm/cmpxchg.h b/arch/s390/include/asm/cmpxchg.h
index 527c968945e8..0b98f57bbe9e 100644
--- a/arch/s390/include/asm/cmpxchg.h
+++ b/arch/s390/include/asm/cmpxchg.h
@@ -173,31 +173,12 @@ static __always_inline u128 arch_cmpxchg128(volatile u128 *ptr, u128 old, u128 n
 {
 	asm volatile(
 		"	cdsg	%[old],%[new],%[ptr]\n"
-		: [old] "+&d" (old)
-		: [new] "d" (new),
-		  [ptr] "QS" (*(u128 *)ptr)
+		: [old] "+d" (old), [ptr] "+QS" (*ptr)
+		: [new] "d" (new)
 		: "memory", "cc");
 	return old;
 }
 
-static __always_inline bool arch_try_cmpxchg128(volatile u128 *ptr, u128 *oldp, u128 new)
-{
-	u128 old = *oldp;
-	int cc;
-
-	asm volatile(
-		"	cdsg	%[old],%[new],%[ptr]\n"
-		"	ipm	%[cc]\n"
-		"	srl	%[cc],28\n"
-		: [cc] "=&d" (cc), [old] "+&d" (old)
-		: [new] "d" (new),
-		  [ptr] "QS" (*(u128 *)ptr)
-		: "memory", "cc");
-
-	if (unlikely(!cc))
-		*oldp = old;
-
-	return likely(cc);
-}
+#define arch_cmpxchg128		arch_cmpxchg128
 
 #endif /* __ASM_CMPXCHG_H */