linux-kernel - Re: [PART1 RFC 9/9] svm: Manage vcpu load/unload when enable AVIC

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Message-ID: <56BDFE63.7010608@redhat.com>
Date:	Fri, 12 Feb 2016 16:46:44 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
	joro@...tes.org, alex.williamson@...hat.com, gleb@...nel.org
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, wei@...hat.com,
	sherry.hurwitz@....com
Subject: Re: [PART1 RFC 9/9] svm: Manage vcpu load/unload when enable AVIC



On 12/02/2016 14:59, Suravee Suthikulpanit wrote:
> +
> +	if (is_running) {
> +		phys_addr_t pa = PFN_PHYS(page_to_pfn(svm->avic_bk_page));
> +
> +		entry->bk_pg_ptr = (pa >> 12) & 0xffffffffff;
> +		entry->valid = 1;
> +		entry->host_phy_apic_id = h_phy_apic_id;
> +		barrier();
> +		entry->is_running = is_running;

I'm not sure if you can rely on the compiler doing the right thing here.
 I would prefer something like:

	new_entry = READ_ONCE(entry);
	new_entry.bk_pg_ptr = (pa >> 12) & 0xffffffffff;
	new_entry.valid = 1;
	new_entry.host_phy_apic_id = h_phy_apic_id;
	new_entry.is_running = is_running;
	WRITE_ONCE(entry, new_entry);

Paolo