[v2][PATCH] kvm: x86: mmio: fix setting the present bit of mmio spte

[v2][PATCH] kvm: x86: mmio: fix setting the present bit of mmio spte

[Tiejun Chen]

In non-ept 64-bit of PAE case maxphyaddr may be 52bit as well,
so we also need to disable mmio page fault. Here we can check
MMIO_SPTE_GEN_HIGH_SHIFT directly to determine if we should
set the present bit, and bring a little cleanup.

Signed-off-by: Tiejun Chen <tiejun.chen@intel.com>
---
v2:

* Correct codes comments
* Need to use "|=" to set the present bit

 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/mmu.c              | 25 +++++++++++++++++++++++++
 arch/x86/kvm/x86.c              | 30 ------------------------------
 3 files changed, 26 insertions(+), 30 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index dc932d3..667f2b6 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -809,6 +809,7 @@ void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,
 				     struct kvm_memory_slot *slot,
 				     gfn_t gfn_offset, unsigned long mask);
 void kvm_mmu_zap_all(struct kvm *kvm);
+void kvm_set_mmio_spte_mask(void);
 void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm);
 unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm);
 void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int kvm_nr_mmu_pages);
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index ac1c4de..fe9a917 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -295,6 +295,31 @@ static bool check_mmio_spte(struct kvm *kvm, u64 spte)
 	return likely(kvm_gen == spte_gen);
 }
 
+/*
+ * Set the reserved bits and the present bit of an paging-structure
+ * entry to generate page fault with PFER.RSV = 1.
+ */
+void kvm_set_mmio_spte_mask(void)
+{
+	u64 mask;
+	int maxphyaddr = boot_cpu_data.x86_phys_bits;
+
+	/* Mask the reserved physical address bits. */
+	mask = rsvd_bits(maxphyaddr, MMIO_SPTE_GEN_HIGH_SHIFT - 1);
+
+	/* Magic bits are always reserved to identify mmio spte.
+	 * On 32 bit systems we have bit 62.
+	 */
+	mask |= 0x3ull << 62;
+
+	/* Set the present bit to enable mmio page fault. */
+	if (maxphyaddr < MMIO_SPTE_GEN_HIGH_SHIFT)
+	    mask |= PT_PRESENT_MASK;
+
+	kvm_mmu_set_mmio_spte_mask(mask);
+}
+EXPORT_SYMBOL_GPL(kvm_set_mmio_spte_mask);
+
 void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask,
 		u64 dirty_mask, u64 nx_mask, u64 x_mask)
 {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f85da5c..550f179 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5596,36 +5596,6 @@ void kvm_after_handle_nmi(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_after_handle_nmi);
 
-static void kvm_set_mmio_spte_mask(void)
-{
-	u64 mask;
-	int maxphyaddr = boot_cpu_data.x86_phys_bits;
-
-	/*
-	 * Set the reserved bits and the present bit of an paging-structure
-	 * entry to generate page fault with PFER.RSV = 1.
-	 */
-	 /* Mask the reserved physical address bits. */
-	mask = rsvd_bits(maxphyaddr, 51);
-
-	/* Bit 62 is always reserved for 32bit host. */
-	mask |= 0x3ull << 62;
-
-	/* Set the present bit. */
-	mask |= 1ull;
-
-#ifdef CONFIG_X86_64
-	/*
-	 * If reserved bit is not supported, clear the present bit to disable
-	 * mmio page fault.
-	 */
-	if (maxphyaddr == 52)
-		mask &= ~1ull;
-#endif
-
-	kvm_mmu_set_mmio_spte_mask(mask);
-}
-
 #ifdef CONFIG_X86_64
 static void pvclock_gtod_update_fn(struct work_struct *work)
 {
-- 
1.9.1

Re: [v2][PATCH] kvm: x86: mmio: fix setting the present bit of mmio spte

[Paolo Bonzini]

On 17/11/2014 12:31, Tiejun Chen wrote:
> In non-ept 64-bit of PAE case maxphyaddr may be 52bit as well,

There is no such thing as 64-bit PAE.

On 32-bit PAE hosts, PTEs have bit 62 reserved, as in your patch:

> +	/* Magic bits are always reserved for 32bit host. */
> +	mask |= 0x3ull << 62;

so there is no need to disable the MMIO page fault.

Paolo

Re: [v2][PATCH] kvm: x86: mmio: fix setting the present bit of mmio spte

[Chen, Tiejun]

On 2014/11/17 19:40, Paolo Bonzini wrote:
>
>
> On 17/11/2014 12:31, Tiejun Chen wrote:
>> In non-ept 64-bit of PAE case maxphyaddr may be 52bit as well,
>
> There is no such thing as 64-bit PAE.
>

Definitely.

> On 32-bit PAE hosts, PTEs have bit 62 reserved, as in your patch:
>

Do you mean just one reserved bit is fine enough in this case?

Thanks
Tiejun

Re: [v2][PATCH] kvm: x86: mmio: fix setting the present bit of mmio spte

[Paolo Bonzini]

On 18/11/2014 10:23, Chen, Tiejun wrote:
>> On 32-bit PAE hosts, PTEs have bit 62 reserved, as in your patch:
> 
> Do you mean just one reserved bit is fine enough in this case?

Yes.

Paolo