| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <4a4d320e-f09c-5198-d3cb-397d837190b1@arm.com>
Date: Wed, 11 Aug 2021 15:07:36 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Marc Zyngier <maz@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org,
James Morse <james.morse@....com>,
Alexandru Elisei <alexandru.elisei@....com>,
Suzuki K Poulose <suzuki.poulose@....com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>, kvmarm@...ts.cs.columbia.edu,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] KVM: arm64: Drop direct PAGE_[SHIFT|SIZE] usage as
page size
On 8/11/21 1:41 PM, Marc Zyngier wrote:
> On Wed, 11 Aug 2021 06:34:46 +0100,
> Anshuman Khandual <anshuman.khandual@....com> wrote:
>>
>>
>>
>> On 8/10/21 7:03 PM, Marc Zyngier wrote:
>>> On 2021-08-10 08:02, Anshuman Khandual wrote:
>>>> 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@...nel.org>
>>>> Cc: James Morse <james.morse@....com>
>>>> Cc: Alexandru Elisei <alexandru.elisei@....com>
>>>> Cc: Suzuki K Poulose <suzuki.poulose@....com>
>>>> Cc: Catalin Marinas <catalin.marinas@....com>
>>>> Cc: Will Deacon <will@...nel.org>
>>>> Cc: linux-arm-kernel@...ts.infradead.org
>>>> Cc: kvmarm@...ts.cs.columbia.edu
>>>> Cc: linux-kernel@...r.kernel.org
>>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>>>> ---
>>>> 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.
>
Powered by blists - more mailing lists