RE: [PATCH 4/6 v5] kvm: powerpc: keep only pte search logic in lookup_linux_pte

-----Original Message-----
From: Alexander Graf [mailto:agraf@suse.de]
Sent: Friday, October 04, 2013 6:57 PM
To: Bhushan Bharat-R65777
Cc: benh@kernel.crashing.org; paulus@samba.org; kvm@vger.kernel.org; kvm-
ppc@vger.kernel.org; linuxppc-dev@lists.ozlabs.org; Wood Scott-B07421; Bh=

ushan

Bharat-R65777
Subject: Re: [PATCH 4/6 v5] kvm: powerpc: keep only pte search logic in
lookup_linux_pte
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On 19.09.2013, at 08:02, Bharat Bhushan wrote:
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quoted

lookup_linux_pte() was searching for a pte and also sets access flags
is writable. This function now searches only pte while access flag
setting is done explicitly.

This pte lookup is not kvm specific, so moved to common code
(asm/pgtable.h) My Followup patch will use this on booke.

Signed-off-by: Bharat Bhushan <redacted>
---
v4->v5
- No change

arch/powerpc/include/asm/pgtable.h  |   24 +++++++++++++++++++++++
arch/powerpc/kvm/book3s_hv_rm_mmu.c |   36 +++++++++++-----------------=

------

quoted

2 files changed, 36 insertions(+), 24 deletions(-)

diff --git a/arch/powerpc/include/asm/pgtable.h

b/arch/powerpc/include/asm/pgtable.h
index 7d6eacf..3a5de5c 100644

--- a/arch/powerpc/include/asm/pgtable.h
+++ b/arch/powerpc/include/asm/pgtable.h

@@ -223,6 +223,30 @@ extern int gup_hugepte(pte_t *ptep, unsigned long

sz, unsigned long addr, #endif pte_t *find_linux_pte_or_hugepte(pgd_t
*pgdir, unsigned long ea,
				 unsigned *shift);
+
+static inline pte_t *lookup_linux_pte(pgd_t *pgdir, unsigned long hva,
+				     unsigned long *pte_sizep)
+{
+	pte_t *ptep;
+	unsigned long ps =3D *pte_sizep;
+	unsigned int shift;
+
+	ptep =3D find_linux_pte_or_hugepte(pgdir, hva, &shift);
+	if (!ptep)
+		return __pte(0);

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This returns a struct pte_t, but your return value of the function is a s=

truct

pte_t *. So this code will fail compiling with STRICT_MM_TYPECHECKS set. =

Any

reason you don't just return NULL here?

I want to return the ptep (pte pointer) , so yes this should be NULL.
Will correct this.

Thanks
-Bharat

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That way callers could simply check on if (ptep) ... or you leave the ret=

urn

value as struct pte_t.
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Alex
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quoted

+	if (shift)
+		*pte_sizep =3D 1ul << shift;
+	else
+		*pte_sizep =3D PAGE_SIZE;
+
+	if (ps > *pte_sizep)
+		return __pte(0);
+
+	if (!pte_present(*ptep))
+		return __pte(0);

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quoted

+
+	return ptep;
+}
#endif /* __ASSEMBLY__ */

#endif /* __KERNEL__ */

diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c

b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
index 45e30d6..74fa7f8 100644

--- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
+++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c

@@ -134,25 +134,6 @@ static void remove_revmap_chain(struct kvm *kvm, l=

ong

pte_index,

quoted

	unlock_rmap(rmap);
}

-static pte_t lookup_linux_pte(pgd_t *pgdir, unsigned long hva,
-			      int writing, unsigned long *pte_sizep)
-{
-	pte_t *ptep;
-	unsigned long ps =3D *pte_sizep;
-	unsigned int hugepage_shift;
-
-	ptep =3D find_linux_pte_or_hugepte(pgdir, hva, &hugepage_shift);
-	if (!ptep)
-		return __pte(0);
-	if (hugepage_shift)
-		*pte_sizep =3D 1ul << hugepage_shift;
-	else
-		*pte_sizep =3D PAGE_SIZE;
-	if (ps > *pte_sizep)
-		return __pte(0);
-	return kvmppc_read_update_linux_pte(ptep, writing, hugepage_shift);
-}
-
static inline void unlock_hpte(unsigned long *hpte, unsigned long
hpte_v) {
	asm volatile(PPC_RELEASE_BARRIER "" : : : "memory"); @@ -173,6 +154,7

@@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,

	unsigned long is_io;
	unsigned long *rmap;
	pte_t pte;
+	pte_t *ptep;
	unsigned int writing;
	unsigned long mmu_seq;
	unsigned long rcbits;

@@ -231,8 +213,9 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned

long flags,

		/* Look up the Linux PTE for the backing page */
		pte_size =3D psize;
-		pte =3D lookup_linux_pte(pgdir, hva, writing, &pte_size);
-		if (pte_present(pte)) {
+		ptep =3D lookup_linux_pte(pgdir, hva, &pte_size);
+		if (pte_present(pte_val(*ptep))) {
+			pte =3D kvmppc_read_update_linux_pte(ptep, writing);
			if (writing && !pte_write(pte))
				/* make the actual HPTE be read-only */
				ptel =3D hpte_make_readonly(ptel);

@@ -661,15 +644,20 @@ long kvmppc_h_protect(struct kvm_vcpu *vcpu, unsi=

gned

long flags,

quoted

			struct kvm_memory_slot *memslot;
			pgd_t *pgdir =3D vcpu->arch.pgdir;
			pte_t pte;
+			pte_t *ptep;

			psize =3D hpte_page_size(v, r);
			gfn =3D ((r & HPTE_R_RPN) & ~(psize - 1)) >> PAGE_SHIFT;
			memslot =3D __gfn_to_memslot(kvm_memslots(kvm), gfn);
			if (memslot) {
				hva =3D __gfn_to_hva_memslot(memslot, gfn);
-				pte =3D lookup_linux_pte(pgdir, hva, 1, &psize);
-				if (pte_present(pte) && !pte_write(pte))
-					r =3D hpte_make_readonly(r);
+				ptep =3D lookup_linux_pte(pgdir, hva, &psize);
+				if (pte_present(pte_val(*ptep))) {
+					pte =3D kvmppc_read_update_linux_pte(ptep,
+									   1);
+					if (pte_present(pte) && !pte_write(pte))
+						r =3D hpte_make_readonly(r);
+				}
			}
		}
	}
--
1.7.0.4


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