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Date: Wed, 11 Dec 2013 15:03:48 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] roms: Flush icache when writing roms to
	guest memory
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To: Alexander Graf <agraf@suse.de>
Cc: "Bogdan.Vlad@freescale.com" <Bogdan.Vlad@freescale.com>, QEMU Developers <qemu-devel@nongnu.org>, "qemu-ppc@nongnu.org" <qemu-ppc@nongnu.org>, "Varun.Sethi@freescale.com" <Varun.Sethi@freescale.com>, Scott Wood <scottwood@freescale.com>, "mihai.caraman@freescale.com" <mihai.caraman@freescale.com>

Il 11/12/2013 14:35, Alexander Graf ha scritto:
>>> >> +            if (kvm_enabled()) {
>>> >> +                /*
>>> >> +                 * The guest may want to directly execute from the rom region,
>>> >> +                 * so we better invalidate its icache
>>> >> +                 */
>>> >> +                flush_icache_range((uintptr_t)ptr, (uintptr_t)ptr + l);
>>> >> +            }
>> > 
>> > Shouldn't KVM itself do that when a memslot is registered?  There should
>> > be no reason for non-TCG QEMU to flush the icache.
> How would KVM know when things changed inside of a memory region? It's up to user space to manage the contents of a memory region, no?

Yeah, that is true.  BTW, shouldn't the same happen when you do migration?

I'd prefer the above snippet to be replaced by a function in
kvm-stub.c/kvm-all.c (kvm_flush_icache_range).

I wonder if there would be a reason to add a KVM_FLUSH_ICACHE ioctl
though.  Could a virtually-indexed/virtually-tagged icache require
flushing by guest address instead of host address?

Paolo