On 08/02/18 11:20, Suzuki K Poulose wrote:
On 07/02/18 15:10, Christoffer Dall wrote:
Hi Suzuki,

On Tue, Jan 09, 2018 at 07:03:57PM +0000, Suzuki K Poulose wrote:
Add helpers for encoding/decoding 52bit address in GICv3 ITS BASER
register. When ITS uses 64K page size, the 52bits of physical address
are encoded in BASER[47:12] as follows :

  Bits[47:16] of the register => bits[47:16] of the physical address
  Bits[15:12] of the register => bits[51:48] of the physical address
                                 bits[15:0] of the physical address are 0.

Also adds a mask for CBASER address. This will be used for adding 52bit
support for VGIC ITS. More importantly ignore the upper bits if 52bit
support is not enabled.

Cc: Shanker Donthineni <shank...@codeaurora.org>
Cc: Marc Zyngier <marc.zyng...@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poul...@arm.com>
---


+
+/*
+ * With 64K page size, the physical address can be upto 52bit and
+ * uses the following encoding in the GITS_BASER[47:12]:
+ *
+ * Bits[47:16] of the register => bits[47:16] of the base physical address. + * Bits[15:12] of the register => bits[51:48] of the base physical address. + *                                bits[15:0] of the base physical address are 0.
+ * Clear the upper bits if the kernel doesn't support 52bits.
+ */
+#define GITS_BASER_ADDR64K_LO_MASK    GENMASK_ULL(47, 16)
+#define GITS_BASER_ADDR64K_HI_SHIFT    12
+#define GITS_BASER_ADDR64K_HI_MOVE    (48 - GITS_BASER_ADDR64K_HI_SHIFT) +#define GITS_BASER_ADDR64K_HI_MASK    (GITS_PA_HI_MASK << GITS_BASER_ADDR64K_HI_SHIFT)
+#define GITS_BASER_ADDR64K_TO_PHYS(x)                    \
+    (((x) & GITS_BASER_ADDR64K_LO_MASK) |                 \
+     (((x) & GITS_BASER_ADDR64K_HI_MASK) << GITS_BASER_ADDR64K_HI_MOVE))
+#define GITS_BASER_ADDR64K_FROM_PHYS(p)                    \
+    (((p) & GITS_BASER_ADDR64K_LO_MASK) |                 \
+     (((p) >> GITS_BASER_ADDR64K_HI_MOVE) & GITS_BASER_ADDR64K_HI_MASK))

I don't understand why you need this masking logic embedded in these
macros?  Isn't it strictly an error if anyone passes a physical address
with any of bits [51:48] set to the ITS on a system that doesn't support
52 bit PAs, and just silently masking off those bits could lead to some
interesting cases.

What do you think is the best way to handle such cases ? May be I could add
some checks where we get those addresses and handle it before we use this
macro ?


This is also notably more difficult to read than the existing macro.

If anything, I think it would be more useful to have
GITS_BASER_TO_PHYS(x) and GITS_PHYS_TO_BASER(x) which takes into account
CONFIG_ARM64_64K_PAGES.

I thought the 64K_PAGES is not kernel page size, but the page-size configured by the "requester" for ITS. So, it doesn't really mean CONFIG_ARM64_64K_PAGES. But the other way around, we can't handle 52bit address unless CONFIG_ARM64_64K_PAGES is selected. Also, if the guest uses a 4K page size and uses a 48 bit address,
we could potentially mask Bits[15:12] to 0, which is not nice.

So I still think we need to have a special macro for handling addresses with 64K
page size in ITS.

If it's allowed to go wrong for invalid input, then you don't even need to consider the page size at all, except if you care about micro-optimising out a couple of instructions. For valid page-aligned addresses, [51:48] and [15:12] can never *both* be nonzero, therefore just this should be fine for all granules:

-       (((phys) & GENMASK_ULL(47, 16)) | (((phys) >> 48) & 0xf) << 12)
+       (((phys) & GENMASK_ULL(47, 0)) | (((phys) >> 48) & 0xf) << 12)

Robin.

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