From: oliver.upton@linux.dev
To: "David Laight" <David.Laight@aculab.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
kvm@vger.kernel.org, Will Deacon <will@kernel.org>,
Marc Zyngier <maz@kernel.org>, Peter Shier <pshier@google.com>,
linux-kernel@vger.kernel.org,
Colton Lewis <coltonlewis@google.com>,
linux-kselftest@vger.kernel.org,
Paolo Bonzini <pbonzini@redhat.com>,
kvmarm@lists.cs.columbia.edu,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] selftests: KVM: Handle compiler optimizations in ucall
Date: Thu, 16 Jun 2022 18:44:53 +0000 [thread overview]
Message-ID: <7b1040c48bc9b2986798322c336660ab@linux.dev> (raw)
In-Reply-To: <3e73cb07968d4c92b797781b037c2d45@AcuMS.aculab.com>
June 16, 2022 11:48 AM, "David Laight" <David.Laight@aculab.com> wrote:
> No wonder I was confused.
> It's not surprising the compiler optimises it all away.
>
> It doesn't seem right to be 'abusing' WRITE_ONCE() here.
> Just adding barrier() should be enough and much more descriptive.
I had the same thought, although I do not believe barrier() is sufficient
on its own. barrier_data() with a pointer to uc passed through
is required to keep clang from eliminating the dead store.
--
Thanks,
Oliver
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
WARNING: multiple messages have this Message-ID (diff)
From: oliver.upton@linux.dev
To: "David Laight" <David.Laight@aculab.com>
Cc: "Raghavendra Rao Ananta" <rananta@google.com>,
"Marc Zyngier" <maz@kernel.org>,
"James Morse" <james.morse@arm.com>,
"Alexandru Elisei" <alexandru.elisei@arm.com>,
"Suzuki K Poulose" <suzuki.poulose@arm.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Catalin Marinas" <catalin.marinas@arm.com>,
"Will Deacon" <will@kernel.org>,
"Peter Shier" <pshier@google.com>,
"Ricardo Koller" <ricarkol@google.com>,
"Oliver Upton" <oupton@google.com>,
"Reiji Watanabe" <reijiw@google.com>,
"Jing Zhang" <jingzhangos@google.com>,
"Colton Lewis" <coltonlewis@google.com>,
linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org, linux-kselftest@vger.kernel.org,
"Andrew Jones" <drjones@redhat.com>
Subject: Re: [PATCH] selftests: KVM: Handle compiler optimizations in ucall
Date: Thu, 16 Jun 2022 18:44:53 +0000 [thread overview]
Message-ID: <7b1040c48bc9b2986798322c336660ab@linux.dev> (raw)
In-Reply-To: <3e73cb07968d4c92b797781b037c2d45@AcuMS.aculab.com>
June 16, 2022 11:48 AM, "David Laight" <David.Laight@aculab.com> wrote:
> No wonder I was confused.
> It's not surprising the compiler optimises it all away.
>
> It doesn't seem right to be 'abusing' WRITE_ONCE() here.
> Just adding barrier() should be enough and much more descriptive.
I had the same thought, although I do not believe barrier() is sufficient
on its own. barrier_data() with a pointer to uc passed through
is required to keep clang from eliminating the dead store.
--
Thanks,
Oliver
WARNING: multiple messages have this Message-ID (diff)
From: oliver.upton@linux.dev
To: "David Laight" <David.Laight@aculab.com>
Cc: "Raghavendra Rao Ananta" <rananta@google.com>,
"Marc Zyngier" <maz@kernel.org>,
"James Morse" <james.morse@arm.com>,
"Alexandru Elisei" <alexandru.elisei@arm.com>,
"Suzuki K Poulose" <suzuki.poulose@arm.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Catalin Marinas" <catalin.marinas@arm.com>,
"Will Deacon" <will@kernel.org>,
"Peter Shier" <pshier@google.com>,
"Ricardo Koller" <ricarkol@google.com>,
"Oliver Upton" <oupton@google.com>,
"Reiji Watanabe" <reijiw@google.com>,
"Jing Zhang" <jingzhangos@google.com>,
"Colton Lewis" <coltonlewis@google.com>,
linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org, linux-kselftest@vger.kernel.org,
"Andrew Jones" <drjones@redhat.com>
Subject: Re: [PATCH] selftests: KVM: Handle compiler optimizations in ucall
Date: Thu, 16 Jun 2022 18:44:53 +0000 [thread overview]
Message-ID: <7b1040c48bc9b2986798322c336660ab@linux.dev> (raw)
In-Reply-To: <3e73cb07968d4c92b797781b037c2d45@AcuMS.aculab.com>
June 16, 2022 11:48 AM, "David Laight" <David.Laight@aculab.com> wrote:
> No wonder I was confused.
> It's not surprising the compiler optimises it all away.
>
> It doesn't seem right to be 'abusing' WRITE_ONCE() here.
> Just adding barrier() should be enough and much more descriptive.
I had the same thought, although I do not believe barrier() is sufficient
on its own. barrier_data() with a pointer to uc passed through
is required to keep clang from eliminating the dead store.
--
Thanks,
Oliver
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2022-06-16 18:45 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-15 18:57 [PATCH] selftests: KVM: Handle compiler optimizations in ucall Raghavendra Rao Ananta
2022-06-15 18:57 ` Raghavendra Rao Ananta
2022-06-15 18:57 ` Raghavendra Rao Ananta
2022-06-16 12:02 ` Andrew Jones
2022-06-16 12:02 ` Andrew Jones
2022-06-16 12:02 ` Andrew Jones
2022-06-16 15:58 ` David Laight
2022-06-16 15:58 ` David Laight
2022-06-16 15:58 ` David Laight
2022-06-16 16:25 ` Andrew Jones
2022-06-16 16:25 ` Andrew Jones
2022-06-16 16:25 ` Andrew Jones
2022-06-16 16:48 ` David Laight
2022-06-16 16:48 ` David Laight
2022-06-16 16:48 ` David Laight
2022-06-16 18:44 ` oliver.upton [this message]
2022-06-16 18:44 ` oliver.upton
2022-06-16 18:44 ` oliver.upton
2022-06-16 21:54 ` David Laight
2022-06-16 21:54 ` David Laight
2022-06-16 21:54 ` David Laight
2022-06-17 7:28 ` Andrew Jones
2022-06-17 7:28 ` Andrew Jones
2022-06-17 7:28 ` Andrew Jones
2022-06-17 9:22 ` Paolo Bonzini
2022-06-17 9:22 ` Paolo Bonzini
2022-06-17 9:22 ` Paolo Bonzini
2022-06-16 12:24 ` Paolo Bonzini
2022-06-16 12:24 ` Paolo Bonzini
2022-06-16 12:24 ` Paolo Bonzini
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