KVM: PPC: Allow for read-only pages backing a Book3S HV guest

With this, if a guest does an H_ENTER with a read/write HPTE on a page
which is currently read-only, we make the actual HPTE inserted be a
read-only version of the HPTE.  We now intercept protection faults as
well as HPTE not found faults, and for a protection fault we work out
whether it should be reflected to the guest (e.g. because the guest HPTE
didn't allow write access to usermode) or handled by switching to
kernel context and calling kvmppc_book3s_hv_page_fault, which will then
request write access to the page and update the actual HPTE.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 18 insertions, 2 deletions

diff --git a/arch/powerpc/include/asm/kvm_book3s_64.h b/arch/powerpc/include/asm/kvm_book3s_64.h
index c21e46da4a3b..b0c08b142770 100644
--- a/arch/powerpc/include/asm/kvm_book3s_64.h
+++ b/arch/powerpc/include/asm/kvm_book3s_64.h
@@ -121,6 +121,22 @@ static inline unsigned long hpte_rpn(unsigned long ptel, unsigned long psize)
 	return ((ptel & HPTE_R_RPN) & ~(psize - 1)) >> PAGE_SHIFT;
 }
 
+static inline int hpte_is_writable(unsigned long ptel)
+{
+	unsigned long pp = ptel & (HPTE_R_PP0 | HPTE_R_PP);
+
+	return pp != PP_RXRX && pp != PP_RXXX;
+}
+
+static inline unsigned long hpte_make_readonly(unsigned long ptel)
+{
+	if ((ptel & HPTE_R_PP0) || (ptel & HPTE_R_PP) == PP_RWXX)
+		ptel = (ptel & ~HPTE_R_PP) | PP_RXXX;
+	else
+		ptel |= PP_RXRX;
+	return ptel;
+}
+
 static inline int hpte_cache_flags_ok(unsigned long ptel, unsigned long io_type)
 {
 	unsigned int wimg = ptel & HPTE_R_WIMG;
@@ -140,7 +156,7 @@ static inline int hpte_cache_flags_ok(unsigned long ptel, unsigned long io_type)
  * Lock and read a linux PTE.  If it's present and writable, atomically
  * set dirty and referenced bits and return the PTE, otherwise return 0.
  */
-static inline pte_t kvmppc_read_update_linux_pte(pte_t *p)
+static inline pte_t kvmppc_read_update_linux_pte(pte_t *p, int writing)
 {
 	pte_t pte, tmp;
 
@@ -158,7 +174,7 @@ static inline pte_t kvmppc_read_update_linux_pte(pte_t *p)
 
 	if (pte_present(pte)) {
 		pte = pte_mkyoung(pte);
-		if (pte_write(pte))
+		if (writing && pte_write(pte))
 			pte = pte_mkdirty(pte);
 	}