Date: Mon, 29 Feb 2016 18:35:46 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Svatopluk Kraus <onwahe@gmail.com> Cc: Justin Hibbits <jrh29@alumni.cwru.edu>, "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: Re: RF_CACHEABLE flag Message-ID: <20160229163545.GW67250@kib.kiev.ua> In-Reply-To: <CAFHCsPVgJt9OJdUtKixGF1XSWtRiD1F8ZHCD5SRodQ77Wm%2B=Sw@mail.gmail.com> References: <CAHSQbTA5A3uSDT143e3yWmfzWZyOCDJ4GSo6JO2NiLc_VAKoYg@mail.gmail.com> <20160222121836.GH91220@kib.kiev.ua> <CAHSQbTDZVpNU0WsXSHM8yuDqn_5vmy9Ox0fnLZLb2NJfoC7Exg@mail.gmail.com> <20160224102754.GK91220@kib.kiev.ua> <CAJ-VmomUxb7nR7cyg58zHVrVP3MB2JLLebWJPf7kB0F7NDpu6A@mail.gmail.com> <CAFHCsPVgJt9OJdUtKixGF1XSWtRiD1F8ZHCD5SRodQ77Wm%2B=Sw@mail.gmail.com>
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On Mon, Feb 29, 2016 at 05:18:16PM +0100, Svatopluk Kraus wrote: > It's not so simple to change memory attributes on ARM. Some conditions > must be met. So, a question is - in which circumstances > pmap_change_attr() is used? > > It's defined like > int pmap_change_attr(vm_offset_t va, vm_size_t size, int mode); > > (1) As memory attributes can be changed on a page basis only, the va > and size are arranged according to that in i386 implementation. That's > okay. > > (2) Can the memory be used by somebody else while the attributes are > being changed? In other words, can the memory be unmapped temporary? Is this for the change of pte through invalidation ? In other words, do you mean, is it fine to temporary unmap the range during the pmap_change_attr() execution ? If yes, it is fine for uses of the function in the DRM code, since it is utilized during a setup of things like GTT or buffers, and no other accesses to the memory could happen until the setup is finished. I noted that function is used by several network drivers as well, and by ntb. It seem that cxgbe and mxge also use it during setup.home | help
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