diff mbox series

[v5,09/19] fixmap: Pass down the full phys address for set_fixmap_io

Message ID 20240819131924.372366-10-steven.price@arm.com (mailing list archive)
State New
Headers show
Series arm64: Support for running as a guest in Arm CCA | expand

Commit Message

Steven Price Aug. 19, 2024, 1:19 p.m. UTC 
From: Suzuki K Poulose <suzuki.poulose@arm.com>

For early I/O mapping using fixmap, we mask the address by PAGE_MASK
base and then map it to the FIXMAP slot. However, with confidential
computing, the granularity at which "protections" (encrypted vs
decrypted) are applied may be finer than the PAGE_SIZE. e.g., for Arm
CCA it is 4K while an arm64 kernel could be using 64K pagesize. However
we need to know the exact address being mapped in.

Thus in-order to calculate the accurate protection, pass down the exact
phys address to the helpers. This would be later used by arm64 to detect
if the MMIO address is shared vs protected. The users of such drivers
already cope with running the same code with "4K" page size, thus
mapping a PAGE_SIZE covering the address range is considered acceptable.

Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
---
New patch for v5
---
 drivers/tty/serial/earlycon.c | 2 +-
 include/asm-generic/fixmap.h  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

Comments

Catalin Marinas Aug. 26, 2024, 10:05 a.m. UTC | #1 
On Mon, Aug 19, 2024 at 02:19:14PM +0100, Steven Price wrote:
> From: Suzuki K Poulose <suzuki.poulose@arm.com>
> 
> For early I/O mapping using fixmap, we mask the address by PAGE_MASK
> base and then map it to the FIXMAP slot. However, with confidential
> computing, the granularity at which "protections" (encrypted vs
> decrypted) are applied may be finer than the PAGE_SIZE. e.g., for Arm
> CCA it is 4K while an arm64 kernel could be using 64K pagesize. However
> we need to know the exact address being mapped in.
> 
> Thus in-order to calculate the accurate protection, pass down the exact
> phys address to the helpers. This would be later used by arm64 to detect
> if the MMIO address is shared vs protected. The users of such drivers
> already cope with running the same code with "4K" page size, thus
> mapping a PAGE_SIZE covering the address range is considered acceptable.
> 
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Steven Price <steven.price@arm.com>

Will was keen (and I'd prefer it as well) to get rid of the early fixmap
code, at least for the time being. Have you tried without these and the
early RSI probing?

Apart from the earlycon I recall you mentioned EFI early maps. These
would be more problematic.
diff mbox series

Patch

diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
index a5fbb6ed38ae..c8414b648d47 100644
--- a/drivers/tty/serial/earlycon.c
+++ b/drivers/tty/serial/earlycon.c
@@ -40,7 +40,7 @@  static void __iomem * __init earlycon_map(resource_size_t paddr, size_t size)
 {
 	void __iomem *base;
 #ifdef CONFIG_FIX_EARLYCON_MEM
-	set_fixmap_io(FIX_EARLYCON_MEM_BASE, paddr & PAGE_MASK);
+	set_fixmap_io(FIX_EARLYCON_MEM_BASE, paddr);
 	base = (void __iomem *)__fix_to_virt(FIX_EARLYCON_MEM_BASE);
 	base += paddr & ~PAGE_MASK;
 #else
diff --git a/include/asm-generic/fixmap.h b/include/asm-generic/fixmap.h
index 9b75fe2bd8fd..8d2222035ed2 100644
--- a/include/asm-generic/fixmap.h
+++ b/include/asm-generic/fixmap.h
@@ -96,7 +96,7 @@  static inline unsigned long virt_to_fix(const unsigned long vaddr)
  */
 #ifndef set_fixmap_io
 #define set_fixmap_io(idx, phys) \
-	__set_fixmap(idx, phys, FIXMAP_PAGE_IO)
+	__set_fixmap(idx, phys & PAGE_MASK, FIXMAP_PAGE_IO)
 #endif
 
 #endif /* __ASSEMBLY__ */