linux-kernel - Re: [PATCH v7 9/9] KVM: arm64: Add support for creating PUD hugepages at stage 2

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Message-ID: <875zyurkz6.fsf@e105922-lin.cambridge.arm.com>
Date:   Tue, 25 Sep 2018 10:21:17 +0100
From:   Punit Agrawal <punit.agrawal@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     <kvmarm@...ts.cs.columbia.edu>, <marc.zyngier@....com>,
        <will.deacon@....com>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Christoffer Dall <christoffer.dall@....com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH v7 9/9] KVM: arm64: Add support for creating PUD hugepages at stage 2

Suzuki K Poulose <suzuki.poulose@....com> writes:

> Hi Punit,
>
>
> On 09/24/2018 06:45 PM, Punit Agrawal wrote:
>> KVM only supports PMD hugepages at stage 2. Now that the various page
>> handling routines are updated, extend the stage 2 fault handling to
>> map in PUD hugepages.
>>
>> Addition of PUD hugepage support enables additional page sizes (e.g.,
>> 1G with 4K granule) which can be useful on cores that support mapping
>> larger block sizes in the TLB entries.
>>
>> Signed-off-by: Punit Agrawal <punit.agrawal@....com>
>> Cc: Christoffer Dall <christoffer.dall@....com>
>> Cc: Marc Zyngier <marc.zyngier@....com>
>> Cc: Russell King <linux@...linux.org.uk>
>> Cc: Catalin Marinas <catalin.marinas@....com>
>> Cc: Will Deacon <will.deacon@....com>
>
>
>>
>> diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
>> index a42b9505c9a7..a8e86b926ee0 100644
>> --- a/arch/arm/include/asm/kvm_mmu.h
>> +++ b/arch/arm/include/asm/kvm_mmu.h
>> @@ -84,11 +84,14 @@ void kvm_clear_hyp_idmap(void);
>>     #define kvm_pfn_pte(pfn, prot)	pfn_pte(pfn, prot)
>>   #define kvm_pfn_pmd(pfn, prot)	pfn_pmd(pfn, prot)
>> +#define kvm_pfn_pud(pfn, prot)	(__pud(0))
>>     #define kvm_pud_pfn(pud)	({ BUG(); 0; })
>>       #define kvm_pmd_mkhuge(pmd)	pmd_mkhuge(pmd)
>> +/* No support for pud hugepages */
>> +#define kvm_pud_mkhuge(pud)	(pud)
>>   
>
> shouldn't this be BUG() like other PUD huge helpers for arm32 ?
>
>>   /*
>>    * The following kvm_*pud*() functions are provided strictly to allow
>> @@ -105,6 +108,23 @@ static inline bool kvm_s2pud_readonly(pud_t *pud)
>>   	return false;
>>   }
>>   +static inline void kvm_set_pud(pud_t *pud, pud_t new_pud)
>> +{
>> +	BUG();
>> +}
>> +
>> +static inline pud_t kvm_s2pud_mkwrite(pud_t pud)
>> +{
>> +	BUG();
>> +	return pud;
>> +}
>> +
>> +static inline pud_t kvm_s2pud_mkexec(pud_t pud)
>> +{
>> +	BUG();
>> +	return pud;
>> +}
>> +
>
>
>> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
>> index 3ff7ebb262d2..5b8163537bc2 100644
>> --- a/virt/kvm/arm/mmu.c
>> +++ b/virt/kvm/arm/mmu.c
>
> ...
>
>
>> @@ -1669,7 +1746,28 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>   	needs_exec = exec_fault ||
>>   		(fault_status == FSC_PERM && stage2_is_exec(kvm, fault_ipa));
>>   -	if (hugetlb && vma_pagesize == PMD_SIZE) {
>> +	if (hugetlb && vma_pagesize == PUD_SIZE) {
>> +		/*
>> +		 * Assuming that PUD level always exists at Stage 2 -
>> +		 * this is true for 4k pages with 40 bits IPA
>> +		 * currently supported.
>> +		 *
>> +		 * When using 64k pages, 40bits of IPA results in
>> +		 * using only 2-levels at Stage 2. Overlooking this
>> +		 * problem for now as a PUD hugepage with 64k pages is
>> +		 * too big (4TB) to be practical.
>> +		 */
>> +		pud_t new_pud = kvm_pfn_pud(pfn, mem_type);
>
> Is this based on the Dynamic IPA series ? The cover letter seems
> to suggest that it is. But I don't see the check to make sure we have
> stage2 PUD level here before we go ahead and try PUD huge page at
> stage2. Also the comment above seems outdated in that case.

It is indeed based on the Dynamic IPA series but I seem to have lost the
actual changes introducing the checks for PUD level. Let me fix that up
and post an update.

Sorry for the noise.

Punit

>
>> +
>> +		new_pud = kvm_pud_mkhuge(new_pud);
>> +		if (writable)
>> +			new_pud = kvm_s2pud_mkwrite(new_pud);
>> +
>> +		if (needs_exec)
>> +			new_pud = kvm_s2pud_mkexec(new_pud);
>> +
>> +		ret = stage2_set_pud_huge(kvm, memcache, fault_ipa, &new_pud);
>> +	} else if (hugetlb && vma_pagesize == PMD_SIZE) {
>>   		pmd_t new_pmd = kvm_pfn_pmd(pfn, mem_type);
>>     		new_pmd = kvm_pmd_mkhuge(new_pmd);
>>
>
>
> Suzuki