[PATCH 0/2] KVM: x86: MMU: Clean up handle_mmio_page_fault() handling in kvm_mmu_page_fault()

[PATCH 0/2] KVM: x86: MMU: Clean up handle_mmio_page_fault() handling in kvm_mmu_page_fault()

[Takuya Yoshikawa]

The end result is very similar to handle_ept_misconfig()'s corresponding code.

It may also be possible to change handle_ept_misconfig() not to call
handle_mmio_page_fault() separately from kvm_mmu_page_fault():
the only difference seems to be whether it checks for PFERR_RSVD_MASK.

Takuya Yoshikawa (2):
  KVM: MMU: Consolidate quickly_check_mmio_pf() and is_mmio_page_fault()
  KVM: MMU: Move handle_mmio_page_fault() call to kvm_mmu_page_fault()

 arch/x86/kvm/mmu.c         | 54 +++++++++++++++++-----------------------------
 arch/x86/kvm/paging_tmpl.h | 19 ++++++----------
 2 files changed, 26 insertions(+), 47 deletions(-)

-- 
2.1.0

[PATCH 1/2] KVM: x86: MMU: Consolidate quickly_check_mmio_pf() and is_mmio_page_fault()

[Takuya Yoshikawa]

These two have only slight differences:
 - whether 'addr' is of type u64 or of type gva_t
 - whether they have 'direct' parameter or not

Concerning the former, quickly_check_mmio_pf()'s u64 is better because
'addr' needs to be able to have both a guest physical address and a
guest virtual address.

The latter is just a stylistic issue as we can always calculate the mode
from the 'vcpu' as is_mmio_page_fault() does.  This patch keeps the
parameter to make the following patch cleaner.

In addition, the patch renames the function to mmio_info_in_cache() to
make it clear what it actually checks for.

Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
---
 arch/x86/kvm/mmu.c | 15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 95a955d..a28b734 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3273,7 +3273,7 @@ static bool is_shadow_zero_bits_set(struct kvm_mmu *mmu, u64 spte, int level)
 	return __is_rsvd_bits_set(&mmu->shadow_zero_check, spte, level);
 }
 
-static bool quickly_check_mmio_pf(struct kvm_vcpu *vcpu, u64 addr, bool direct)
+static bool mmio_info_in_cache(struct kvm_vcpu *vcpu, u64 addr, bool direct)
 {
 	if (direct)
 		return vcpu_match_mmio_gpa(vcpu, addr);
@@ -3332,7 +3332,7 @@ int handle_mmio_page_fault(struct kvm_vcpu *vcpu, u64 addr, bool direct)
 	u64 spte;
 	bool reserved;
 
-	if (quickly_check_mmio_pf(vcpu, addr, direct))
+	if (mmio_info_in_cache(vcpu, addr, direct))
 		return RET_MMIO_PF_EMULATE;
 
 	reserved = walk_shadow_page_get_mmio_spte(vcpu, addr, &spte);
@@ -4354,19 +4354,12 @@ static void make_mmu_pages_available(struct kvm_vcpu *vcpu)
 	kvm_mmu_commit_zap_page(vcpu->kvm, &invalid_list);
 }
 
-static bool is_mmio_page_fault(struct kvm_vcpu *vcpu, gva_t addr)
-{
-	if (vcpu->arch.mmu.direct_map || mmu_is_nested(vcpu))
-		return vcpu_match_mmio_gpa(vcpu, addr);
-
-	return vcpu_match_mmio_gva(vcpu, addr);
-}
-
 int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u32 error_code,
 		       void *insn, int insn_len)
 {
 	int r, emulation_type = EMULTYPE_RETRY;
 	enum emulation_result er;
+	bool direct = vcpu->arch.mmu.direct_map || mmu_is_nested(vcpu);
 
 	r = vcpu->arch.mmu.page_fault(vcpu, cr2, error_code, false);
 	if (r < 0)
@@ -4377,7 +4370,7 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u32 error_code,
 		goto out;
 	}
 
-	if (is_mmio_page_fault(vcpu, cr2))
+	if (mmio_info_in_cache(vcpu, cr2, direct))
 		emulation_type = 0;
 
 	er = x86_emulate_instruction(vcpu, cr2, emulation_type, insn, insn_len);
-- 
2.1.0

[PATCH 2/2] KVM: x86: MMU: Move handle_mmio_page_fault() call to kvm_mmu_page_fault()

[Takuya Yoshikawa]

Rather than placing a handle_mmio_page_fault() call in each
vcpu->arch.mmu.page_fault() handler, moving it up to
kvm_mmu_page_fault() makes the code better:

 - avoids code duplication
 - for kvm_arch_async_page_ready(), which is the other caller of
   vcpu->arch.mmu.page_fault(), removes an extra error_code check
 - avoids returning both RET_MMIO_PF_* values and raw integer values
   from vcpu->arch.mmu.page_fault()

Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
---
 arch/x86/kvm/mmu.c         | 39 ++++++++++++++++-----------------------
 arch/x86/kvm/paging_tmpl.h | 19 ++++++-------------
 2 files changed, 22 insertions(+), 36 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index a28b734..2ce3892 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3370,13 +3370,6 @@ static int nonpaging_page_fault(struct kvm_vcpu *vcpu, gva_t gva,
 
 	pgprintk("%s: gva %lx error %x\n", __func__, gva, error_code);
 
-	if (unlikely(error_code & PFERR_RSVD_MASK)) {
-		r = handle_mmio_page_fault(vcpu, gva, true);
-
-		if (likely(r != RET_MMIO_PF_INVALID))
-			return r;
-	}
-
 	r = mmu_topup_memory_caches(vcpu);
 	if (r)
 		return r;
@@ -3460,13 +3453,6 @@ static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa, u32 error_code,
 
 	MMU_WARN_ON(!VALID_PAGE(vcpu->arch.mmu.root_hpa));
 
-	if (unlikely(error_code & PFERR_RSVD_MASK)) {
-		r = handle_mmio_page_fault(vcpu, gpa, true);
-
-		if (likely(r != RET_MMIO_PF_INVALID))
-			return r;
-	}
-
 	r = mmu_topup_memory_caches(vcpu);
 	if (r)
 		return r;
@@ -4361,18 +4347,27 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u32 error_code,
 	enum emulation_result er;
 	bool direct = vcpu->arch.mmu.direct_map || mmu_is_nested(vcpu);
 
+	if (unlikely(error_code & PFERR_RSVD_MASK)) {
+		r = handle_mmio_page_fault(vcpu, cr2, direct);
+		if (r == RET_MMIO_PF_EMULATE) {
+			emulation_type = 0;
+			goto emulate;
+		}
+		if (r == RET_MMIO_PF_RETRY)
+			return 1;
+		if (r < 0)
+			return r;
+	}
+
 	r = vcpu->arch.mmu.page_fault(vcpu, cr2, error_code, false);
 	if (r < 0)
-		goto out;
-
-	if (!r) {
-		r = 1;
-		goto out;
-	}
+		return r;
+	if (!r)
+		return 1;
 
 	if (mmio_info_in_cache(vcpu, cr2, direct))
 		emulation_type = 0;
-
+emulate:
 	er = x86_emulate_instruction(vcpu, cr2, emulation_type, insn, insn_len);
 
 	switch (er) {
@@ -4386,8 +4381,6 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u32 error_code,
 	default:
 		BUG();
 	}
-out:
-	return r;
 }
 EXPORT_SYMBOL_GPL(kvm_mmu_page_fault);
 
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 6c9fed9..05827ff 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -702,24 +702,17 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
 
 	pgprintk("%s: addr %lx err %x\n", __func__, addr, error_code);
 
-	if (unlikely(error_code & PFERR_RSVD_MASK)) {
-		r = handle_mmio_page_fault(vcpu, addr, mmu_is_nested(vcpu));
-		if (likely(r != RET_MMIO_PF_INVALID))
-			return r;
-
-		/*
-		 * page fault with PFEC.RSVD  = 1 is caused by shadow
-		 * page fault, should not be used to walk guest page
-		 * table.
-		 */
-		error_code &= ~PFERR_RSVD_MASK;
-	};
-
 	r = mmu_topup_memory_caches(vcpu);
 	if (r)
 		return r;
 
 	/*
+	 * If PFEC.RSVD is set, this is a shadow page fault.
+	 * The bit needs to be cleared before walking guest page tables.
+	 */
+	error_code &= ~PFERR_RSVD_MASK;
+
+	/*
 	 * Look up the guest pte for the faulting address.
 	 */
 	r = FNAME(walk_addr)(&walker, vcpu, addr, error_code);
-- 
2.1.0

Re: [PATCH 2/2] KVM: x86: MMU: Move handle_mmio_page_fault() call to kvm_mmu_page_fault()

[Paolo Bonzini]

On 22/02/2016 09:23, Takuya Yoshikawa wrote:
> Rather than placing a handle_mmio_page_fault() call in each
> vcpu->arch.mmu.page_fault() handler, moving it up to
> kvm_mmu_page_fault() makes the code better:
> 
>  - avoids code duplication
>  - for kvm_arch_async_page_ready(), which is the other caller of
>    vcpu->arch.mmu.page_fault(), removes an extra error_code check
>  - avoids returning both RET_MMIO_PF_* values and raw integer values
>    from vcpu->arch.mmu.page_fault()
> 
> Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
> ---
>  arch/x86/kvm/mmu.c         | 39 ++++++++++++++++-----------------------
>  arch/x86/kvm/paging_tmpl.h | 19 ++++++-------------
>  2 files changed, 22 insertions(+), 36 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index a28b734..2ce3892 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -3370,13 +3370,6 @@ static int nonpaging_page_fault(struct kvm_vcpu *vcpu, gva_t gva,
>  
>  	pgprintk("%s: gva %lx error %x\n", __func__, gva, error_code);
>  
> -	if (unlikely(error_code & PFERR_RSVD_MASK)) {
> -		r = handle_mmio_page_fault(vcpu, gva, true);
> -
> -		if (likely(r != RET_MMIO_PF_INVALID))
> -			return r;
> -	}
> -
>  	r = mmu_topup_memory_caches(vcpu);
>  	if (r)
>  		return r;
> @@ -3460,13 +3453,6 @@ static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa, u32 error_code,
>  
>  	MMU_WARN_ON(!VALID_PAGE(vcpu->arch.mmu.root_hpa));
>  
> -	if (unlikely(error_code & PFERR_RSVD_MASK)) {
> -		r = handle_mmio_page_fault(vcpu, gpa, true);
> -
> -		if (likely(r != RET_MMIO_PF_INVALID))
> -			return r;
> -	}
> -
>  	r = mmu_topup_memory_caches(vcpu);
>  	if (r)
>  		return r;
> @@ -4361,18 +4347,27 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u32 error_code,
>  	enum emulation_result er;
>  	bool direct = vcpu->arch.mmu.direct_map || mmu_is_nested(vcpu);
>  
> +	if (unlikely(error_code & PFERR_RSVD_MASK)) {
> +		r = handle_mmio_page_fault(vcpu, cr2, direct);
> +		if (r == RET_MMIO_PF_EMULATE) {
> +			emulation_type = 0;
> +			goto emulate;
> +		}
> +		if (r == RET_MMIO_PF_RETRY)
> +			return 1;
> +		if (r < 0)
> +			return r;

It's a bit weird how RET_MMIO_PF_RETRY is zero, but unifying all the
return values of page fault routines is best left for another day.

Applied to queue, thanks.

Paolo

> +	}
> +
>  	r = vcpu->arch.mmu.page_fault(vcpu, cr2, error_code, false);
>  	if (r < 0)
> -		goto out;
> -
> -	if (!r) {
> -		r = 1;
> -		goto out;
> -	}
> +		return r;
> +	if (!r)
> +		return 1;
>  
>  	if (mmio_info_in_cache(vcpu, cr2, direct))
>  		emulation_type = 0;
> -
> +emulate:
>  	er = x86_emulate_instruction(vcpu, cr2, emulation_type, insn, insn_len);
>  
>  	switch (er) {
> @@ -4386,8 +4381,6 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u32 error_code,
>  	default:
>  		BUG();
>  	}
> -out:
> -	return r;
>  }
>  EXPORT_SYMBOL_GPL(kvm_mmu_page_fault);
>  
> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> index 6c9fed9..05827ff 100644
> --- a/arch/x86/kvm/paging_tmpl.h
> +++ b/arch/x86/kvm/paging_tmpl.h
> @@ -702,24 +702,17 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
>  
>  	pgprintk("%s: addr %lx err %x\n", __func__, addr, error_code);
>  
> -	if (unlikely(error_code & PFERR_RSVD_MASK)) {
> -		r = handle_mmio_page_fault(vcpu, addr, mmu_is_nested(vcpu));
> -		if (likely(r != RET_MMIO_PF_INVALID))
> -			return r;
> -
> -		/*
> -		 * page fault with PFEC.RSVD  = 1 is caused by shadow
> -		 * page fault, should not be used to walk guest page
> -		 * table.
> -		 */
> -		error_code &= ~PFERR_RSVD_MASK;
> -	};
> -
>  	r = mmu_topup_memory_caches(vcpu);
>  	if (r)
>  		return r;
>  
>  	/*
> +	 * If PFEC.RSVD is set, this is a shadow page fault.
> +	 * The bit needs to be cleared before walking guest page tables.
> +	 */
> +	error_code &= ~PFERR_RSVD_MASK;
> +
> +	/*
>  	 * Look up the guest pte for the faulting address.
>  	 */
>  	r = FNAME(walk_addr)(&walker, vcpu, addr, error_code);
>