Re: [Qemu-devel] [PATCH] KVM: always use MADV_DONTFORK

From: Peter Maydell <peter.maydell@linaro.org>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	qemu-devel@nongnu.org, Gleb Natapov <gleb@redhat.com>,
	qemu-stable@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] KVM: always use MADV_DONTFORK
Date: Thu, 25 Jul 2013 11:16:44 +0100	[thread overview]
Message-ID: <CAFEAcA8vb3+n+F3=VfX204HnEmCrc9Db+e=V-zeqG_eySb7VDA@mail.gmail.com> (raw)
In-Reply-To: <1374747075-7172-1-git-send-email-aarcange@redhat.com>

On 25 July 2013 11:11, Andrea Arcangeli <aarcange@redhat.com> wrote:
> diff --git a/exec.c b/exec.c
> index c99a883..d3bb58d 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1162,6 +1162,7 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
>
>      qemu_ram_setup_dump(new_block->host, size);
>      qemu_madvise(new_block->host, size, QEMU_MADV_HUGEPAGE);
> +    qemu_madvise(new_block->host, size, QEMU_MADV_DONTFORK);
>
>      if (kvm_enabled())
>          kvm_setup_guest_memory(new_block->host, size);
>

kvm_setup_guest_memory() already calls
  qemu_madvise(start, size, QEMU_MADV_DONTFORK)
so why do we need to do it here as well?
If we should be doing it in all cases presumably the right
fix is to move the if (!kvm_has_sync_mmu()) check in
kvm_setup_guest_memory() from "do we call madvise" to
"do we fail with an error if it failed".

thanks
-- PMM