On 8/11/21 1:41 PM, Marc Zyngier wrote:

On Wed, 11 Aug 2021 06:34:46 +0100,
Anshuman Khandual [off-list ref] wrote:

quoted

On 8/10/21 7:03 PM, Marc Zyngier wrote:

quoted

On 2021-08-10 08:02, Anshuman Khandual wrote:

quoted

All instances here could just directly test against CONFIG_ARM64_XXK_PAGES
instead of evaluating via PAGE_SHIFT or PAGE_SIZE. With this change, there
will be no such usage left.

Cc: Marc Zyngier <maz@kernel.org>
Cc: James Morse <james.morse@arm.com>
Cc: Alexandru Elisei <redacted>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: kvmarm@lists.cs.columbia.edu
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <redacted>
---
 arch/arm64/kvm/hyp/pgtable.c | 6 +++---
 arch/arm64/mm/mmu.c          | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 05321f4165e3..a6112b6d6ef6 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c

@@ -85,7 +85,7 @@ static bool kvm_level_supports_block_mapping(u32 level)

      * Reject invalid block mappings and don't bother with 4TB mappings for
      * 52-bit PAs.
      */
-    return !(level == 0 || (PAGE_SIZE != SZ_4K && level == 1));
+    return !(level == 0 || (!IS_ENABLED(CONFIG_ARM64_4K_PAGES) && level == 1));
 }

 static bool kvm_block_mapping_supported(u64 addr, u64 end, u64 phys, u32 level)

@@ -155,7 +155,7 @@ static u64 kvm_pte_to_phys(kvm_pte_t pte)

 {
     u64 pa = pte & KVM_PTE_ADDR_MASK;

-    if (PAGE_SHIFT == 16)
+    if (IS_ENABLED(CONFIG_ARM64_64K_PAGES))
         pa |= FIELD_GET(KVM_PTE_ADDR_51_48, pte) << 48;

     return pa;

@@ -165,7 +165,7 @@ static kvm_pte_t kvm_phys_to_pte(u64 pa)

 {
     kvm_pte_t pte = pa & KVM_PTE_ADDR_MASK;

-    if (PAGE_SHIFT == 16)
+    if (IS_ENABLED(CONFIG_ARM64_64K_PAGES))
         pte |= FIELD_PREP(KVM_PTE_ADDR_51_48, pa >> 48);

     return pte;

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 9ff0de1b2b93..8fdfca179815 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c

@@ -296,7 +296,7 @@ static void alloc_init_cont_pmd(pud_t *pudp,

unsigned long addr,
 static inline bool use_1G_block(unsigned long addr, unsigned long next,
             unsigned long phys)
 {
-    if (PAGE_SHIFT != 12)
+    if (!IS_ENABLED(CONFIG_ARM64_4K_PAGES))
         return false;

     if (((addr | next | phys) & ~PUD_MASK) != 0)

I personally find it a lot less readable.

Also, there is no evaluation whatsoever. All the code guarded
by a PAGE_SIZE/PAGE_SHIFT that doesn't match the configuration
is dropped at compile time.

The primary idea here is to unify around IS_ENABLED(CONFIG_ARM64_XXK_PAGES)
usage in arm64, rather than having multiple methods to test page size when
ever required.

I'm sorry, but I find the idiom extremely painful to parse. If you are

Okay, it was not explained very well. My bad.

annoyed with the 'PAGE_SHIFT == 12/14/16', consider replacing it with
'PAGE_SIZE == SZ_4/16/64K' instead.

Sure, understood. But the problem here is not with PAGE_SHIFT/PAGE_SIZE
based tests but rather having multiple ways of doing the same thing in
arm64 tree. Please find further explanation below.

IS_ENABLED(CONFIG_ARM64_XXK_PAGES) also gives the wrong impression
that *multiple* page sizes can be selected at any given time. That's
obviously not the case, which actually makes PAGE_SIZE a much better
choice.

PAGE_SHIFT and PAGE_SIZE are derived from CONFIG_ARM64_XXK_PAGES. Hence
why not just directly use the original user selected config option that
eventually decides PAGE_SHIFT and PAGE_SIZE.

config ARM64_PAGE_SHIFT
        int
        default 16 if ARM64_64K_PAGES
        default 14 if ARM64_16K_PAGES
        default 12

arch/arm64/include/asm/page-def.h:#define PAGE_SHIFT	CONFIG_ARM64_PAGE_SHIFT
arch/arm64/include/asm/page-def.h:#define PAGE_SIZE	(_AC(1, UL) << PAGE_SHIFT)

Also there are already similar IS_ENABLED() instances which do not
create much confusion. The point here being, to have just a single
method that checks compiled page size support, instead of three
different ways of doing the same thing.

- IS_ENABLED(CONFIG_ARM64_XXK_PAGES)
- if (PAGE_SHIFT == XX)
- if (PAGE_SIZE == XX)

$git grep IS_ENABLED arch/arm64/ | grep PAGES

arch/arm64/include/asm/vmalloc.h:	return IS_ENABLED(CONFIG_ARM64_4K_PAGES) &&
arch/arm64/mm/mmu.c:		BUG_ON(!IS_ENABLED(CONFIG_ARM64_16K_PAGES));
arch/arm64/mm/mmu.c:		BUG_ON(!IS_ENABLED(CONFIG_ARM64_16K_PAGES));

As things stand, I don't plan to take such a patch.

Sure, will drop it from the series if the above explanation and
the rationale for the patch still does not convince you.

Thanks,

	M.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel