[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <9B7F4808-2294-426D-B463-CEB188CED2E0@gmail.com>
Date: Fri, 14 Oct 2016 12:44:53 -0700
From: Nadav Amit <nadav.amit@...il.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>,
Radim Krčmář <rkrcmar@...hat.com>,
Yang Zhang <yang.zhang.wz@...il.com>,
feng wu <feng.wu@...el.com>, mst@...hat.com
Subject: Re: [PATCH 1/5] KVM: x86: avoid atomic operations on APICv vmentry
> On Oct 14, 2016, at 11:56 AM, Paolo Bonzini <pbonzini@...hat.com> wrote:
>>>
>>> for (i = 0; i <= 7; i++) {
>>> - pir_val = xchg(&pir[i], 0);
>>> - if (pir_val)
>>> + pir_val = READ_ONCE(pir[i]);
>>
>> Out of curiosity, do you really need this READ_ONCE?
>
> The answer can only be "depends on the compiler's whims". :)
> If you think of READ_ONCE as a C11 relaxed atomic load, then yes.
Hm.. So the idea is to make the code "race-free” in the sense
that every concurrent memory access is done using READ_ONCE/WRITE_ONCE?
If that is the case, I think there are many other cases that need to be
changed, for example apic->irr_pending and vcpu->arch.pv.pv_unhalted.
Powered by blists - more mailing lists