Re: [Xen-devel] [PATCH v4 6/7] x86 / vmx: use a MEMF_no_refcount domheap page for APIC_DEFAULT_PHYS_BASE

From: Jan Beulich <jbeulich@suse.com>
To: Paul Durrant <pdurrant@amazon.com>
Cc: "Kevin Tian" <kevin.tian@intel.com>, "Wei Liu" <wl@xen.org>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Jun Nakajima" <jun.nakajima@intel.com>,
	xen-devel@lists.xenproject.org,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH v4 6/7] x86 / vmx: use a MEMF_no_refcount domheap page for APIC_DEFAULT_PHYS_BASE
Date: Tue, 28 Jan 2020 16:23:55 +0100	[thread overview]
Message-ID: <db575271-12fa-a905-c5b7-72f6aae941e1@suse.com> (raw)
In-Reply-To: <20200124153103.18321-7-pdurrant@amazon.com>

On 24.01.2020 16:31, Paul Durrant wrote:
> vmx_alloc_vlapic_mapping() currently contains some very odd looking code
> that allocates a MEMF_no_owner domheap page and then shares with the guest
> as if it were a xenheap page. This then requires vmx_free_vlapic_mapping()
> to call a special function in the mm code: free_shared_domheap_page().
> 
> By using a MEMF_no_refcount domheap page instead, the odd looking code in
> vmx_alloc_vlapic_mapping() can simply use get_page_and_type() to set up a
> writable mapping before insertion in the P2M and vmx_free_vlapic_mapping()
> can simply release the page using put_page_alloc_ref() followed by
> put_page_and_type(). This then allows free_shared_domheap_page() to be
> purged.
> 
> Signed-off-by: Paul Durrant <pdurrant@amazon.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>


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