linux-kernel - Re: [PATCH 04/11] powerpc/kvm: Don't store values derivable from HPT order

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Date:   Mon, 19 Dec 2016 11:04:56 +1100
From:   David Gibson <david@...son.dropbear.id.au>
To:     Thomas Huth <thuth@...hat.com>
Cc:     paulus@...ba.org, michael@...erman.id.au, benh@...nel.crashing.org,
        sjitindarsingh@...il.com, lvivier@...hat.com,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH 04/11] powerpc/kvm: Don't store values derivable from HPT
 order

On Fri, Dec 16, 2016 at 11:39:26AM +0100, Thomas Huth wrote:
> On 15.12.2016 06:53, David Gibson wrote:
> > Currently the kvm_hpt_info structure stores the hashed page table's order,
> > and also the number of HPTEs it contains and a mask for its size.  The
> > last two can be easily derived from the order, so remove them and just
> > calculate them as necessary with a couple of helper inlines.
> > 
> > Signed-off-by: David Gibson <david@...son.dropbear.id.au>
> > ---
> [...]
> > diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> > index b5799d1..fe88132 100644
> > --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> > +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> > @@ -83,15 +83,11 @@ long kvmppc_alloc_hpt(struct kvm *kvm, u32 *htab_orderp)
> >  
> >  	kvm->arch.hpt.virt = hpt;
> >  	kvm->arch.hpt.order = order;
> > -	/* HPTEs are 2**4 bytes long */
> > -	kvm->arch.hpt.npte = 1ul << (order - 4);
> > -	/* 128 (2**7) bytes in each HPTEG */
> > -	kvm->arch.hpt.mask = (1ul << (order - 7)) - 1;
> >  
> >  	atomic64_set(&kvm->arch.mmio_update, 0);
> >  
> >  	/* Allocate reverse map array */
> > -	rev = vmalloc(sizeof(struct revmap_entry) * kvm->arch.hpt.npte);
> > +	rev = vmalloc(sizeof(struct revmap_entry) * kvmppc_hpt_npte(&kvm->arch.hpt));
> >  	if (!rev) {
> >  		pr_err("kvmppc_alloc_hpt: Couldn't alloc reverse map array\n");
> >  		goto out_freehpt;
> > @@ -194,8 +190,8 @@ void kvmppc_map_vrma(struct kvm_vcpu *vcpu, struct kvm_memory_slot *memslot,
> >  	if (npages > 1ul << (40 - porder))
> >  		npages = 1ul << (40 - porder);
> >  	/* Can't use more than 1 HPTE per HPTEG */
> > -	if (npages > kvm->arch.hpt.mask + 1)
> > -		npages = kvm->arch.hpt.mask + 1;
> > +	if (npages > kvmppc_hpt_mask(&kvm->arch.hpt) + 1)
> > +		npages = kvmppc_hpt_mask(&kvm->arch.hpt) + 1;
> >  
> >  	hp0 = HPTE_V_1TB_SEG | (VRMA_VSID << (40 - 16)) |
> >  		HPTE_V_BOLTED | hpte0_pgsize_encoding(psize);
> > @@ -205,7 +201,8 @@ void kvmppc_map_vrma(struct kvm_vcpu *vcpu, struct kvm_memory_slot *memslot,
> >  	for (i = 0; i < npages; ++i) {
> >  		addr = i << porder;
> >  		/* can't use hpt_hash since va > 64 bits */
> > -		hash = (i ^ (VRMA_VSID ^ (VRMA_VSID << 25))) & kvm->arch.hpt.mask;
> > +		hash = (i ^ (VRMA_VSID ^ (VRMA_VSID << 25)))
> > +			& kvmppc_hpt_mask(&kvm->arch.hpt);
> >  		/*
> >  		 * We assume that the hash table is empty and no
> >  		 * vcpus are using it at this stage.  Since we create
> 
> kvmppc_hpt_mask() is now called three times in kvmppc_map_vrma() ... you
> could use a local variable to store the value so that the calculation
> has only be done once here.

Well, I was assuming that inlining plus gcc's common subexpression
elimination would deal with that.

> 
> > @@ -1306,7 +1303,7 @@ static ssize_t kvm_htab_read(struct file *file, char __user *buf,
> >  
> >  		/* Skip uninteresting entries, i.e. clean on not-first pass */
> >  		if (!first_pass) {
> > -			while (i < kvm->arch.hpt.npte &&
> > +			while (i < kvmppc_hpt_npte(&kvm->arch.hpt) &&
> >  			       !hpte_dirty(revp, hptp)) {
> >  				++i;
> >  				hptp += 2;
> > @@ -1316,7 +1313,7 @@ static ssize_t kvm_htab_read(struct file *file, char __user *buf,
> >  		hdr.index = i;
> >  
> >  		/* Grab a series of valid entries */
> > -		while (i < kvm->arch.hpt.npte &&
> > +		while (i < kvmppc_hpt_npte(&kvm->arch.hpt) &&
> >  		       hdr.n_valid < 0xffff &&
> >  		       nb + HPTE_SIZE < count &&
> >  		       record_hpte(flags, hptp, hpte, revp, 1, first_pass)) {
> > @@ -1332,7 +1329,7 @@ static ssize_t kvm_htab_read(struct file *file, char __user *buf,
> >  			++revp;
> >  		}
> >  		/* Now skip invalid entries while we can */
> > -		while (i < kvm->arch.hpt.npte &&
> > +		while (i < kvmppc_hpt_npte(&kvm->arch.hpt) &&
> >  		       hdr.n_invalid < 0xffff &&
> >  		       record_hpte(flags, hptp, hpte, revp, 0, first_pass)) {
> >  			/* found an invalid entry */
> 
> Dito, you could use a local variable to store the value from
> kvmppc_hpt_npte()
> 
> Anyway, apart from these nits, patch looks fine to me, so:
> 
> Reviewed-by: Thomas Huth <thuth@...hat.com>
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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