Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <af294653-ae7b-7fdf-695a-5e48108e795f@arm.com>
Date:   Fri, 16 Dec 2022 05:01:29 +0530
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.2.2
Subject: Re: [PATCH] arm64: errata: refer to config ARM64_ERRATUM_2645198 to
 make workaround work
Content-Language: en-US
To:     Will Deacon <will@kernel.org>
Cc:     Lukas Bulwahn <lukas.bulwahn@gmail.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        linux-arm-kernel@lists.infradead.org,
        kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20221215094811.23188-1-lukas.bulwahn@gmail.com>
 <20221215105745.GA7711@willie-the-truck>
 <b6f61241-e436-5db1-1053-3b441080b8d6@arm.com>
 <20221215194413.GA8094@willie-the-truck>
From:   Anshuman Khandual <anshuman.khandual@arm.com>
In-Reply-To: <20221215194413.GA8094@willie-the-truck>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 12/16/22 01:14, Will Deacon wrote:
> On Thu, Dec 15, 2022 at 04:59:20PM +0530, Anshuman Khandual wrote:
>> On 12/15/22 16:27, Will Deacon wrote:
>>> On Thu, Dec 15, 2022 at 10:48:11AM +0100, Lukas Bulwahn wrote:
>>>> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
>>>> index cd8d96e1fa1a..95364e8bdc19 100644
>>>> --- a/arch/arm64/mm/hugetlbpage.c
>>>> +++ b/arch/arm64/mm/hugetlbpage.c
>>>> @@ -562,7 +562,7 @@ bool __init arch_hugetlb_valid_size(unsigned long size)
>>>>  
>>>>  pte_t huge_ptep_modify_prot_start(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep)
>>>>  {
>>>> -	if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198) &&
>>>> +	if (IS_ENABLED(CONFIG_ARM64_ERRATUM_2645198) &&
>>>>  	    cpus_have_const_cap(ARM64_WORKAROUND_2645198)) {
>>>>  		/*
>>>>  		 * Break-before-make (BBM) is required for all user space mappings
>>>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>>>> index 12915f379c22..d77c9f56b7b4 100644
>>>> --- a/arch/arm64/mm/mmu.c
>>>> +++ b/arch/arm64/mm/mmu.c
>>>> @@ -1633,7 +1633,7 @@ early_initcall(prevent_bootmem_remove_init);
>>>>  
>>>>  pte_t ptep_modify_prot_start(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep)
>>>>  {
>>>> -	if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198) &&
>>>> +	if (IS_ENABLED(CONFIG_ARM64_ERRATUM_2645198) &&
>>>>  	    cpus_have_const_cap(ARM64_WORKAROUND_2645198)) {
>>>>  		/*
>>>>  		 * Break-before-make (BBM) is required for all user space mappings
>>>
>>> Grr, this bug seems to exist in all three versions of the patch reviewed on
>>> the list, so I can only draw the conclusion that this code has never been
>>
>> Ohh, my bad, apologies. I did not have a real system with this erratum, although
>> had emulated and tested this workaround path via some other debug changes (which
>> might have just forced the first condition to always evaluate true).
> 
> "might have"?
> 
>>> tested. Consequently, I'm more inclined to _revert_ the change for now and
>>> we can bring it back as a fix once somebody has checked that it actually
>>> works properly.
>> Please do not revert this change if possible.
> 
> I've gone ahead with the revert anyway, just because it's the easy thing to
> do and we can bring back a fixed version of the patch as a fix in the new
> year. So please send a new version with this fix folded in after you've
> tested that it doesn't cause regressions for systems without the erratum.

Sure, will resend. Again, apologies for this last minute merge window trouble.