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Message-ID: <5af478e1da6c0b847fbaf3aff6ccce5720e8a23c.camel@linux.ibm.com>
Subject: Re: [PATCH 1/1] powerpc: kvm: Reduce calls to get current->mm by
 storing the value locally
From:   Leonardo Bras <leonardo@linux.ibm.com>
To:     PaulMackerras <paulus@samba.org>, linuxppc-dev@lists.ozlabs.org,
        linux-kernel@vger.kernel.org
Date:   Thu, 19 Sep 2019 23:47:36 -0300
In-Reply-To: <20190919222748.20761-1-leonardo@linux.ibm.com>
References: <20190919222748.20761-1-leonardo@linux.ibm.com>
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Hello Paul,=20
I sent this patch, but I have a question:

On Thu, 2019-09-19 at 19:27 -0300, Leonardo Bras wrote:
> Reduces the number of calls to get_current() in order to get the value of
> current->mm by doing it once and storing the value, since it is not
> supposed to change inside the same process).
>=20
> Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
> ---
>  arch/powerpc/kvm/book3s_64_mmu_hv.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>=20
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3=
s_64_mmu_hv.c
> index 9a75f0e1933b..f2b9aea43216 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> @@ -508,6 +508,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, =
struct kvm_vcpu *vcpu,
>  	struct vm_area_struct *vma;
>  	unsigned long rcbits;
>  	long mmio_update;
> +	struct mm_struct *mm;
> =20
>  	if (kvm_is_radix(kvm))
>  		return kvmppc_book3s_radix_page_fault(run, vcpu, ea, dsisr);
> @@ -584,6 +585,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, =
struct kvm_vcpu *vcpu,
>  	is_ci =3D false;
>  	pfn =3D 0;
>  	page =3D NULL;
> +	mm =3D current->mm;

Here, current->mm is not always the same as kvm->mm?=20

>  	pte_size =3D PAGE_SIZE;
>  	writing =3D (dsisr & DSISR_ISSTORE) !=3D 0;
>  	/* If writing !=3D 0, then the HPTE must allow writing, if we get here =
*/
> @@ -592,8 +594,8 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, =
struct kvm_vcpu *vcpu,
>  	npages =3D get_user_pages_fast(hva, 1, writing ? FOLL_WRITE : 0, pages)=
;
>  	if (npages < 1) {
>  		/* Check if it's an I/O mapping */
> -		down_read(&current->mm->mmap_sem);
> -		vma =3D find_vma(current->mm, hva);
> +		down_read(&mm->mmap_sem);
> +		vma =3D find_vma(mm, hva);
>  		if (vma && vma->vm_start <=3D hva && hva + psize <=3D vma->vm_end &&
>  		    (vma->vm_flags & VM_PFNMAP)) {
>  			pfn =3D vma->vm_pgoff +
> @@ -602,7 +604,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, =
struct kvm_vcpu *vcpu,
>  			is_ci =3D pte_ci(__pte((pgprot_val(vma->vm_page_prot))));
>  			write_ok =3D vma->vm_flags & VM_WRITE;
>  		}
> -		up_read(&current->mm->mmap_sem);
> +		up_read(&mm->mmap_sem);
>  		if (!pfn)
>  			goto out_put;
>  	} else {
> @@ -621,8 +623,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, =
struct kvm_vcpu *vcpu,
>  			 * hugepage split and collapse.
>  			 */
>  			local_irq_save(flags);
> -			ptep =3D find_current_mm_pte(current->mm->pgd,
> -						   hva, NULL, NULL);
> +			ptep =3D find_current_mm_pte(mm->pgd, hva, NULL, NULL);
>  			if (ptep) {
>  				pte =3D kvmppc_read_update_linux_pte(ptep, 1);
>  				if (__pte_write(pte))

Thanks !

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