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Date: Thu, 5 Jul 2018 17:24:14 +0100
From: Marc Zyngier <marc.zyngier@....com>
To: Punit Agrawal <punit.agrawal@....com>, kvmarm@...ts.cs.columbia.edu
Cc: linux-arm-kernel@...ts.infradead.org, christoffer.dall@....com,
linux-kernel@...r.kernel.org, suzuki.poulose@....com
Subject: Re: [PATCH v4 1/7] KVM: arm/arm64: Share common code in
user_mem_abort()
Hi Punit,
On 05/07/18 15:08, Punit Agrawal wrote:
> The code for operations such as marking the pfn as dirty, and
> dcache/icache maintenance during stage 2 fault handling is duplicated
> between normal pages and PMD hugepages.
>
> Instead of creating another copy of the operations when we introduce
> PUD hugepages, let's share them across the different pagesizes.
>
> Signed-off-by: Punit Agrawal <punit.agrawal@....com>
> Cc: Christoffer Dall <christoffer.dall@....com>
> Cc: Marc Zyngier <marc.zyngier@....com>
> ---
> virt/kvm/arm/mmu.c | 68 +++++++++++++++++++++++++++-------------------
> 1 file changed, 40 insertions(+), 28 deletions(-)
>
> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
> index 1d90d79706bd..dd14cc36c51c 100644
> --- a/virt/kvm/arm/mmu.c
> +++ b/virt/kvm/arm/mmu.c
> @@ -1398,6 +1398,21 @@ static void invalidate_icache_guest_page(kvm_pfn_t pfn, unsigned long size)
> __invalidate_icache_guest_page(pfn, size);
> }
>
> +static bool stage2_should_exec(struct kvm *kvm, phys_addr_t addr,
> + bool exec_fault, unsigned long fault_status)
I find this "should exec" very confusing.
> +{
> + /*
> + * If we took an execution fault we will have made the
> + * icache/dcache coherent and should now let the s2 mapping be
> + * executable.
> + *
> + * Write faults (!exec_fault && FSC_PERM) are orthogonal to
> + * execute permissions, and we preserve whatever we have.
> + */
> + return exec_fault ||
> + (fault_status == FSC_PERM && stage2_is_exec(kvm, addr));
> +}
> +
> static void kvm_send_hwpoison_signal(unsigned long address,
> struct vm_area_struct *vma)
> {
> @@ -1431,7 +1446,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> kvm_pfn_t pfn;
> pgprot_t mem_type = PAGE_S2;
> bool logging_active = memslot_is_logging(memslot);
> - unsigned long flags = 0;
> + unsigned long vma_pagesize, flags = 0;
>
> write_fault = kvm_is_write_fault(vcpu);
> exec_fault = kvm_vcpu_trap_is_iabt(vcpu);
> @@ -1451,7 +1466,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> return -EFAULT;
> }
>
> - if (vma_kernel_pagesize(vma) == PMD_SIZE && !logging_active) {
> + vma_pagesize = vma_kernel_pagesize(vma);
> + if (vma_pagesize == PMD_SIZE && !logging_active) {
> hugetlb = true;
> gfn = (fault_ipa & PMD_MASK) >> PAGE_SHIFT;
> } else {
> @@ -1520,28 +1536,34 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> if (mmu_notifier_retry(kvm, mmu_seq))
> goto out_unlock;
>
> - if (!hugetlb && !force_pte)
> + if (!hugetlb && !force_pte) {
> + /*
> + * Only PMD_SIZE transparent hugepages(THP) are
> + * currently supported. This code will need to be
> + * updated to support other THP sizes.
> + */
> hugetlb = transparent_hugepage_adjust(&pfn, &fault_ipa);
> + if (hugetlb)
> + vma_pagesize = PMD_SIZE;
> + }
> +
> + if (writable)
> + kvm_set_pfn_dirty(pfn);
>
> - if (hugetlb) {
> + if (fault_status != FSC_PERM)
> + clean_dcache_guest_page(pfn, vma_pagesize);
> +
> + if (exec_fault)
> + invalidate_icache_guest_page(pfn, vma_pagesize);
> +
> + if (hugetlb && vma_pagesize == PMD_SIZE) {
> pmd_t new_pmd = pfn_pmd(pfn, mem_type);
> new_pmd = pmd_mkhuge(new_pmd);
> - if (writable) {
> + if (writable)
> new_pmd = kvm_s2pmd_mkwrite(new_pmd);
> - kvm_set_pfn_dirty(pfn);
> - }
>
> - if (fault_status != FSC_PERM)
> - clean_dcache_guest_page(pfn, PMD_SIZE);
> -
> - if (exec_fault) {
> + if (stage2_should_exec(kvm, fault_ipa, exec_fault, fault_status))
> new_pmd = kvm_s2pmd_mkexec(new_pmd);
OK, I find this absolutely horrid... ;-)
The rest of the function deals with discrete flags, and all of a sudden
we have a function call with a bunch of seemingly unrelated parameters.
And you are repeating it for each vma_pagesize...
How about something like:
bool needs_exec;
[...]
needs_exec = exec_fault || (fault_status == FSC_PERM &&
stage2_is_exec(kvm, fault_ipa);
And then you just check needs_exec to update the pte/pmd. And you drop
this helper.
> - invalidate_icache_guest_page(pfn, PMD_SIZE);
> - } else if (fault_status == FSC_PERM) {
> - /* Preserve execute if XN was already cleared */
> - if (stage2_is_exec(kvm, fault_ipa))
> - new_pmd = kvm_s2pmd_mkexec(new_pmd);
> - }
>
> ret = stage2_set_pmd_huge(kvm, memcache, fault_ipa, &new_pmd);
> } else {
> @@ -1549,21 +1571,11 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>
> if (writable) {
> new_pte = kvm_s2pte_mkwrite(new_pte);
> - kvm_set_pfn_dirty(pfn);
> mark_page_dirty(kvm, gfn);
> }
>
> - if (fault_status != FSC_PERM)
> - clean_dcache_guest_page(pfn, PAGE_SIZE);
> -
> - if (exec_fault) {
> + if (stage2_should_exec(kvm, fault_ipa, exec_fault, fault_status))
> new_pte = kvm_s2pte_mkexec(new_pte);
> - invalidate_icache_guest_page(pfn, PAGE_SIZE);
> - } else if (fault_status == FSC_PERM) {
> - /* Preserve execute if XN was already cleared */
> - if (stage2_is_exec(kvm, fault_ipa))
> - new_pte = kvm_s2pte_mkexec(new_pte);
> - }
>
> ret = stage2_set_pte(kvm, memcache, fault_ipa, &new_pte, flags);
> }
>
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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