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Re: [Xen-devel] [PATCH 3/8] xen/arm: Implement p2m_type_t as an enum
On 12/05/2013 04:56 PM, Ian Campbell wrote:
On Thu, 2013-12-05 at 16:44 +0000, Julien Grall wrote:
On 12/05/2013 04:38 PM, Ian Campbell wrote:
On Thu, 2013-12-05 at 16:28 +0000, Julien Grall wrote:
On 12/05/2013 04:14 PM, Ian Campbell wrote:
On Thu, 2013-12-05 at 16:01 +0000, Julien Grall wrote:
On 12/05/2013 03:52 PM, Ian Campbell wrote:
On Thu, 2013-12-05 at 15:42 +0000, Julien Grall wrote:
Until now, Xen doesn't know the type of the page (ram, foreign page, mmio,...).
Introduce p2m_type_t with basic types:
- p2m_invalid: Nothing is mapped here
Do we really need this? Is it not equivalent to not setting the present
bit? I see x86 has the same type though -- Tim can you explain why.
We need a default value when Xen retrieves the p2m type. I don't think
we can assume that p2m_ram_rw (or any other type) is used by default.
Since the avail bits in the p2m pte are in pretty short supply I think
we can avoid unnecessary types.
I plan to use directly the decimal value. So we can store up to 16 values.
16 is short supply in my book ;-)
Having got a bit further through the series I see how p2m_invalid is
being used now. It is a useful pseudo-type but it doesn't need to be
represented in the avail bits I don't think. How about:
typedef enum {
p2m_ram_rw, /* Normal read/write guest RAM */
p2m_ram_ro, /* Read-only; writes are silently dropped */
p2m_mmio_direct, /* Read/write mapping of genuine MMIO area /
p2m_map_foreign, /* Ram pages from foreign domain */
p2m_max_real_type = 16, /* Types after this are pseudo-types. */
p2m_invalid, /* Nothing mapped here */
} p2m_type_t;
BUILD_BUG_ON(p2m_max_real_type >= 2^4);
Now you can return it etc but it never needs to get put in an actual
pte?
This solution was easier to avoid extra code in the different function.
I will rework it for the next series.
"This" is what I suggested here or what you wrote already?
The code I wrote.
Maybe we should just keep this trick in our pocket for when we run out
of bits then?
Sounds good to me. I will add a comment in the code with your solution.
--
Julien Grall
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