[PATCH 1/2] KVM: MMU: fix SMAP virtualization

[PATCH 1/2] KVM: MMU: fix SMAP virtualization

[Xiao Guangrong]

KVM may turn a user page to a kernel page when kernel writes a readonly
user page if CR0.WP = 1. This shadow page entry will be reused after
SMAP is enabled so that kernel is allowed to access this user page

Fix it by setting SMAP && !CR0.WP into shadow page's role and reset mmu
once CR4.SMAP is updated

Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/mmu.c              | 16 ++++++++++++----
 arch/x86/kvm/mmu.h              |  2 --
 arch/x86/kvm/x86.c              |  8 +++-----
 4 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 8b661d1..bbb8f4e 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -207,6 +207,7 @@ union kvm_mmu_page_role {
 		unsigned nxe:1;
 		unsigned cr0_wp:1;
 		unsigned smep_andnot_wp:1;
+		unsigned smap_andnot_wp:1;
 	};
 };
 
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 3711095..b78e83f 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3737,8 +3737,8 @@ static void reset_rsvds_bits_mask_ept(struct kvm_vcpu *vcpu,
 	}
 }
 
-void update_permission_bitmask(struct kvm_vcpu *vcpu,
-		struct kvm_mmu *mmu, bool ept)
+static void update_permission_bitmask(struct kvm_vcpu *vcpu,
+				      struct kvm_mmu *mmu, bool ept)
 {
 	unsigned bit, byte, pfec;
 	u8 map;
@@ -3919,6 +3919,7 @@ static void init_kvm_tdp_mmu(struct kvm_vcpu *vcpu)
 void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu)
 {
 	bool smep = kvm_read_cr4_bits(vcpu, X86_CR4_SMEP);
+	bool smap = kvm_read_cr4_bits(vcpu, X86_CR4_SMAP);
 	struct kvm_mmu *context = &vcpu->arch.mmu;
 
 	MMU_WARN_ON(VALID_PAGE(context->root_hpa));
@@ -3937,6 +3938,8 @@ void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu)
 	context->base_role.cr0_wp  = is_write_protection(vcpu);
 	context->base_role.smep_andnot_wp
 		= smep && !is_write_protection(vcpu);
+	context->base_role.smap_andnot_wp
+		= smap && !is_write_protection(vcpu);
 }
 EXPORT_SYMBOL_GPL(kvm_init_shadow_mmu);
 
@@ -4208,12 +4211,18 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
 		       const u8 *new, int bytes)
 {
 	gfn_t gfn = gpa >> PAGE_SHIFT;
-	union kvm_mmu_page_role mask = { .word = 0 };
 	struct kvm_mmu_page *sp;
 	LIST_HEAD(invalid_list);
 	u64 entry, gentry, *spte;
 	int npte;
 	bool remote_flush, local_flush, zap_page;
+	union kvm_mmu_page_role mask = (union kvm_mmu_page_role) {
+		.cr0_wp = 1,
+		.cr4_pae = 1,
+		.nxe = 1,
+		.smep_andnot_wp = 1,
+		.smap_andnot_wp = 1,
+	};
 
 	/*
 	 * If we don't have indirect shadow pages, it means no page is
@@ -4239,7 +4248,6 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
 	++vcpu->kvm->stat.mmu_pte_write;
 	kvm_mmu_audit(vcpu, AUDIT_PRE_PTE_WRITE);
 
-	mask.cr0_wp = mask.cr4_pae = mask.nxe = mask.smep_andnot_wp = 1;
 	for_each_gfn_indirect_valid_sp(vcpu->kvm, sp, gfn) {
 		if (detect_write_misaligned(sp, gpa, bytes) ||
 		      detect_write_flooding(sp)) {
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 06eb2fc..0ada65e 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -71,8 +71,6 @@ enum {
 int handle_mmio_page_fault_common(struct kvm_vcpu *vcpu, u64 addr, bool direct);
 void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu);
 void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly);
-void update_permission_bitmask(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
-		bool ept);
 
 static inline unsigned int kvm_mmu_available_pages(struct kvm *kvm)
 {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cdccbe1..cde5d61 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -702,8 +702,9 @@ EXPORT_SYMBOL_GPL(kvm_set_xcr);
 int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 {
 	unsigned long old_cr4 = kvm_read_cr4(vcpu);
-	unsigned long pdptr_bits = X86_CR4_PGE | X86_CR4_PSE |
-				   X86_CR4_PAE | X86_CR4_SMEP;
+	unsigned long pdptr_bits = X86_CR4_PGE | X86_CR4_PSE | X86_CR4_PAE |
+				   X86_CR4_SMEP | X86_CR4_SMAP;
+
 	if (cr4 & CR4_RESERVED_BITS)
 		return 1;
 
@@ -744,9 +745,6 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 	    (!(cr4 & X86_CR4_PCIDE) && (old_cr4 & X86_CR4_PCIDE)))
 		kvm_mmu_reset_context(vcpu);
 
-	if ((cr4 ^ old_cr4) & X86_CR4_SMAP)
-		update_permission_bitmask(vcpu, vcpu->arch.walk_mmu, false);
-
 	if ((cr4 ^ old_cr4) & X86_CR4_OSXSAVE)
 		kvm_update_cpuid(vcpu);
 
-- 
2.1.0

[PATCH 2/2] KVM: MMU: document smap_andnot_wp

[Xiao Guangrong]

Document this new role field

Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
---
 Documentation/virtual/kvm/mmu.txt | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/Documentation/virtual/kvm/mmu.txt b/Documentation/virtual/kvm/mmu.txt
index 53838d9..c59bd9b 100644
--- a/Documentation/virtual/kvm/mmu.txt
+++ b/Documentation/virtual/kvm/mmu.txt
@@ -169,6 +169,10 @@ Shadow pages contain the following information:
     Contains the value of cr4.smep && !cr0.wp for which the page is valid
     (pages for which this is true are different from other pages; see the
     treatment of cr0.wp=0 below).
+  role.smap_andnot_wp:
+    Contains the value of cr4.smap && !cr0.wp for which the page is valid
+    (pages for which this is true are different from other pages; see the
+    treatment of cr0.wp=0 below).
   gfn:
     Either the guest page table containing the translations shadowed by this
     page, or the base page frame for linear translations.  See role.direct.
@@ -344,10 +348,16 @@ on fault type:
 
 (user write faults generate a #PF)
 
-In the first case there is an additional complication if CR4.SMEP is
-enabled: since we've turned the page into a kernel page, the kernel may now
-execute it.  We handle this by also setting spte.nx.  If we get a user
-fetch or read fault, we'll change spte.u=1 and spte.nx=gpte.nx back.
+In the first case there are two additional complications:
+- if CR4.SMEP is enabled: since we've turned the page into a kernel page,
+  the kernel may now execute it.  We handle this by also setting spte.nx.
+  If we get a user fetch or read fault, we'll change spte.u=1 and
+  spte.nx=gpte.nx back.
+- if CR4.SMAP is disabled: since the page has been changed to a kernel
+  page, it can not be reused when CR4.SMAP is enabled. We set
+  CR4.SMAP && !CR0.WP into shadow page's role to avoid this case. Note,
+  here we do not care the case that CR4.SMAP is enabled since KVM will
+  directly inject #PF to guest due to failed permission check.
 
 To prevent an spte that was converted into a kernel page with cr0.wp=0
 from being written by the kernel after cr0.wp has changed to 1, we make
-- 
2.1.0

Re: [PATCH 2/2] KVM: MMU: document smap_andnot_wp

[Paolo Bonzini]

On 11/05/2015 16:55, Xiao Guangrong wrote:
> Document this new role field
> 
> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
> ---
>  Documentation/virtual/kvm/mmu.txt | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/virtual/kvm/mmu.txt b/Documentation/virtual/kvm/mmu.txt
> index 53838d9..c59bd9b 100644
> --- a/Documentation/virtual/kvm/mmu.txt
> +++ b/Documentation/virtual/kvm/mmu.txt
> @@ -169,6 +169,10 @@ Shadow pages contain the following information:
>      Contains the value of cr4.smep && !cr0.wp for which the page is valid
>      (pages for which this is true are different from other pages; see the
>      treatment of cr0.wp=0 below).
> +  role.smap_andnot_wp:
> +    Contains the value of cr4.smap && !cr0.wp for which the page is valid
> +    (pages for which this is true are different from other pages; see the
> +    treatment of cr0.wp=0 below).
>    gfn:
>      Either the guest page table containing the translations shadowed by this
>      page, or the base page frame for linear translations.  See role.direct.
> @@ -344,10 +348,16 @@ on fault type:
>  
>  (user write faults generate a #PF)
>  
> -In the first case there is an additional complication if CR4.SMEP is
> -enabled: since we've turned the page into a kernel page, the kernel may now
> -execute it.  We handle this by also setting spte.nx.  If we get a user
> -fetch or read fault, we'll change spte.u=1 and spte.nx=gpte.nx back.
> +In the first case there are two additional complications:
> +- if CR4.SMEP is enabled: since we've turned the page into a kernel page,
> +  the kernel may now execute it.  We handle this by also setting spte.nx.
> +  If we get a user fetch or read fault, we'll change spte.u=1 and
> +  spte.nx=gpte.nx back.
> +- if CR4.SMAP is disabled: since the page has been changed to a kernel
> +  page, it can not be reused when CR4.SMAP is enabled. We set
> +  CR4.SMAP && !CR0.WP into shadow page's role to avoid this case. Note,
> +  here we do not care the case that CR4.SMAP is enabled since KVM will
> +  directly inject #PF to guest due to failed permission check.
>  
>  To prevent an spte that was converted into a kernel page with cr0.wp=0
>  from being written by the kernel after cr0.wp has changed to 1, we make
> 

Thanks, squashed with 1/2 and both applied.

Paolo

Re: [PATCH 1/2] KVM: MMU: fix SMAP virtualization

[Boris Ostrovsky]

On 05/11/2015 10:55 AM, Xiao Guangrong wrote:
> KVM may turn a user page to a kernel page when kernel writes a readonly
> user page if CR0.WP = 1. This shadow page entry will be reused after
> SMAP is enabled so that kernel is allowed to access this user page
>
> Fix it by setting SMAP && !CR0.WP into shadow page's role and reset mmu
> once CR4.SMAP is updated
>
> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
> ---


>
> @@ -4208,12 +4211,18 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
>   		       const u8 *new, int bytes)
>   {
>   	gfn_t gfn = gpa >> PAGE_SHIFT;
> -	union kvm_mmu_page_role mask = { .word = 0 };
>   	struct kvm_mmu_page *sp;
>   	LIST_HEAD(invalid_list);
>   	u64 entry, gentry, *spte;
>   	int npte;
>   	bool remote_flush, local_flush, zap_page;
> +	union kvm_mmu_page_role mask = (union kvm_mmu_page_role) {
> +		.cr0_wp = 1,
> +		.cr4_pae = 1,
> +		.nxe = 1,
> +		.smep_andnot_wp = 1,
> +		.smap_andnot_wp = 1,
> +	};
>
>


This breaks older compilers that can't initialize anon structures.

-boris

Re: [PATCH 1/2] KVM: MMU: fix SMAP virtualization

[Bandan Das]

Boris Ostrovsky <boris.ostrovsky@oracle.com> writes:

> On 05/11/2015 10:55 AM, Xiao Guangrong wrote:
>> KVM may turn a user page to a kernel page when kernel writes a readonly
>> user page if CR0.WP = 1. This shadow page entry will be reused after
>> SMAP is enabled so that kernel is allowed to access this user page
>>
>> Fix it by setting SMAP && !CR0.WP into shadow page's role and reset mmu
>> once CR4.SMAP is updated
>>
>> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
>> ---
>
>
>>
>> @@ -4208,12 +4211,18 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
>>   		       const u8 *new, int bytes)
>>   {
>>   	gfn_t gfn = gpa >> PAGE_SHIFT;
>> -	union kvm_mmu_page_role mask = { .word = 0 };
>>   	struct kvm_mmu_page *sp;
>>   	LIST_HEAD(invalid_list);
>>   	u64 entry, gentry, *spte;
>>   	int npte;
>>   	bool remote_flush, local_flush, zap_page;
>> +	union kvm_mmu_page_role mask = (union kvm_mmu_page_role) {
>> +		.cr0_wp = 1,
>> +		.cr4_pae = 1,
>> +		.nxe = 1,
>> +		.smep_andnot_wp = 1,
>> +		.smap_andnot_wp = 1,
>> +	};
>>
>>
>
>
> This breaks older compilers that can't initialize anon structures.

How old ? Even gcc 3.1 says you can use unnamed struct/union fields and
3.2 is the minimum version required to compile the kernel as mentioned
in the README.

We could simply just name the structure, but I doubt this is the
only place in the kernel code where it's being used this way :)

Bandan

> -boris
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Re: [PATCH 1/2] KVM: MMU: fix SMAP virtualization

[Boris Ostrovsky]

On 05/22/2015 07:54 PM, Bandan Das wrote:
> Boris Ostrovsky <boris.ostrovsky@oracle.com> writes:
>
>> On 05/11/2015 10:55 AM, Xiao Guangrong wrote:
>>> KVM may turn a user page to a kernel page when kernel writes a readonly
>>> user page if CR0.WP = 1. This shadow page entry will be reused after
>>> SMAP is enabled so that kernel is allowed to access this user page
>>>
>>> Fix it by setting SMAP && !CR0.WP into shadow page's role and reset mmu
>>> once CR4.SMAP is updated
>>>
>>> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
>>> ---
>>
>>
>>>
>>> @@ -4208,12 +4211,18 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
>>>    		       const u8 *new, int bytes)
>>>    {
>>>    	gfn_t gfn = gpa >> PAGE_SHIFT;
>>> -	union kvm_mmu_page_role mask = { .word = 0 };
>>>    	struct kvm_mmu_page *sp;
>>>    	LIST_HEAD(invalid_list);
>>>    	u64 entry, gentry, *spte;
>>>    	int npte;
>>>    	bool remote_flush, local_flush, zap_page;
>>> +	union kvm_mmu_page_role mask = (union kvm_mmu_page_role) {
>>> +		.cr0_wp = 1,
>>> +		.cr4_pae = 1,
>>> +		.nxe = 1,
>>> +		.smep_andnot_wp = 1,
>>> +		.smap_andnot_wp = 1,
>>> +	};
>>>
>>>
>>
>>
>> This breaks older compilers that can't initialize anon structures.
>
> How old ? Even gcc 3.1 says you can use unnamed struct/union fields and
> 3.2 is the minimum version required to compile the kernel as mentioned
> in the README.
>
> We could simply just name the structure, but I doubt this is the
> only place in the kernel code where it's being used this way :)


You can use them but you can't use initializers. Unfortunately my build 
system (F13) conveniently went down but this is an example from an old 
email:

FC-64 <build@build-mk2:~/xtt-x86_64/bootstrap> cat anon.c
struct bar {
struct {
int i;
};
};

main()
{
struct bar a = {.i = 0};
}

FC-64 <build@build-mk2:~/xtt-x86_64/bootstrap> gcc --version|head -1
gcc (GCC) 4.4.4 20100503 (Red Hat 4.4.4-2)
FC-64 <build@build-mk2:~/xtt-x86_64/bootstrap> gcc anon.c
anon.c: In function ‘main’:
anon.c:9: error: unknown field ‘i’ specified in initializer
FC-64 <build@build-mk2:~/xtt-x86_64/bootstrap>


but

build@build-mk2 bootstrap]$ gcc --version|head -1
gcc (GCC) 4.6.3 20120306 (Red Hat 4.6.3-2)
[build@build-mk2 bootstrap]$ gcc anon.c
[build@build-mk2 bootstrap]$


-boris

Re: [PATCH 1/2] KVM: MMU: fix SMAP virtualization

[Edward Cree]

>> This breaks older compilers that can't initialize anon structures.
> 
> How old ? Even gcc 3.1 says you can use unnamed struct/union fields and
> 3.2 is the minimum version required to compile the kernel as mentioned
> in the README.
> 
> We could simply just name the structure, but I doubt this is the
> only place in the kernel code where it's being used this way :)

This appears to be GCC bug #10676, see <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=10676>
Says it was fixed in 4.6, but I believe the kernel supports GCCs much older
than that (back to 3.2).  I personally hit it on 4.4.7, the version shipped
with RHEL6.6.
So I think the kernel code has to change, probably by naming the structure.

Re: [PATCH 1/2] KVM: MMU: fix SMAP virtualization

[Paolo Bonzini]

On 26/05/2015 16:45, Edward Cree wrote:
>>> This breaks older compilers that can't initialize anon structures.
>> >
>> > How old ? Even gcc 3.1 says you can use unnamed struct/union fields and
>> > 3.2 is the minimum version required to compile the kernel as mentioned
>> > in the README.
>> >
>> > We could simply just name the structure, but I doubt this is the
>> > only place in the kernel code where it's being used this way :)
> This appears to be GCC bug #10676, see <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=10676>
> Says it was fixed in 4.6, but I believe the kernel supports GCCs much older
> than that (back to 3.2).  I personally hit it on 4.4.7, the version shipped
> with RHEL6.6.

Yes, it will be fixed soon(ish).  Probably before you can get rid of the
obnoxious disclaimer... :)

Paolo

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Re: [PATCH 1/2] KVM: MMU: fix SMAP virtualization

[Xiao Guangrong]

On 05/26/2015 10:48 PM, Paolo Bonzini wrote:
>
>
> On 26/05/2015 16:45, Edward Cree wrote:
>>>> This breaks older compilers that can't initialize anon structures.
>>>>
>>>> How old ? Even gcc 3.1 says you can use unnamed struct/union fields and
>>>> 3.2 is the minimum version required to compile the kernel as mentioned
>>>> in the README.
>>>>
>>>> We could simply just name the structure, but I doubt this is the
>>>> only place in the kernel code where it's being used this way :)
>> This appears to be GCC bug #10676, see <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=10676>
>> Says it was fixed in 4.6, but I believe the kernel supports GCCs much older
>> than that (back to 3.2).  I personally hit it on 4.4.7, the version shipped
>> with RHEL6.6.
>
> Yes, it will be fixed soon(ish).  Probably before you can get rid of the
> obnoxious disclaimer... :)

It has been fixed by Andrew:

From: Andrew Morton <akpm@linux-foundation.org>
Subject: arch/x86/kvm/mmu.c: work around gcc-4.4.4 bug

arch/x86/kvm/mmu.c: In function 'kvm_mmu_pte_write':
arch/x86/kvm/mmu.c:4256: error: unknown field 'cr0_wp' specified in initializer
arch/x86/kvm/mmu.c:4257: error: unknown field 'cr4_pae' specified in initializer
arch/x86/kvm/mmu.c:4257: warning: excess elements in union initializer
...

gcc-4.4.4 (at least) has issues when using anonymous unions in
initializers.

Fixes: edc90b7dc4ceef6 ("KVM: MMU: fix SMAP virtualization")
Cc: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Should be found at -mm tree.

Re: [PATCH 1/2] KVM: MMU: fix SMAP virtualization

[Vinson Lee]

On Tue, May 26, 2015 at 7:53 PM, Xiao Guangrong
<guangrong.xiao@linux.intel.com> wrote:
>
>
> On 05/26/2015 10:48 PM, Paolo Bonzini wrote:
>>
>>
>>
>> On 26/05/2015 16:45, Edward Cree wrote:
>>>>>
>>>>> This breaks older compilers that can't initialize anon structures.
>>>>>
>>>>> How old ? Even gcc 3.1 says you can use unnamed struct/union fields and
>>>>> 3.2 is the minimum version required to compile the kernel as mentioned
>>>>> in the README.
>>>>>
>>>>> We could simply just name the structure, but I doubt this is the
>>>>> only place in the kernel code where it's being used this way :)
>>>
>>> This appears to be GCC bug #10676, see
>>> <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=10676>
>>> Says it was fixed in 4.6, but I believe the kernel supports GCCs much
>>> older
>>> than that (back to 3.2).  I personally hit it on 4.4.7, the version
>>> shipped
>>> with RHEL6.6.
>>
>>
>> Yes, it will be fixed soon(ish).  Probably before you can get rid of the
>> obnoxious disclaimer... :)
>
>
> It has been fixed by Andrew:
>
> From: Andrew Morton <akpm@linux-foundation.org>
> Subject: arch/x86/kvm/mmu.c: work around gcc-4.4.4 bug
>
> arch/x86/kvm/mmu.c: In function 'kvm_mmu_pte_write':
> arch/x86/kvm/mmu.c:4256: error: unknown field 'cr0_wp' specified in
> initializer
> arch/x86/kvm/mmu.c:4257: error: unknown field 'cr4_pae' specified in
> initializer
> arch/x86/kvm/mmu.c:4257: warning: excess elements in union initializer
> ...
>
> gcc-4.4.4 (at least) has issues when using anonymous unions in
> initializers.
>
> Fixes: edc90b7dc4ceef6 ("KVM: MMU: fix SMAP virtualization")
> Cc: Xiao Guangrong <guangrong.xiao@linux.intel.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
>
> Should be found at -mm tree.
>
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Hi.

Please backport "arch/x86/kvm/mmu.c: work around gcc-4.4.4 bug" to
stable trees that have backported "KVM: MMU: fix SMAP virtualization".

Currently, the Linux 4.0.5 build is broken with GCC 4.4.

"KVM: MMU: fix SMAP virtualization" is currently queued for 3.16.y-ckt
and 3.18.y.

Cheers,
Vinson

Re: [PATCH 1/2] KVM: MMU: fix SMAP virtualization

[Davidlohr Bueso]

On Wed, 2015-05-27 at 10:53 +0800, Xiao Guangrong wrote:
> 
> On 05/26/2015 10:48 PM, Paolo Bonzini wrote:
> >
> >
> > On 26/05/2015 16:45, Edward Cree wrote:
> >>>> This breaks older compilers that can't initialize anon structures.
> >>>>
> >>>> How old ? Even gcc 3.1 says you can use unnamed struct/union fields and
> >>>> 3.2 is the minimum version required to compile the kernel as mentioned
> >>>> in the README.
> >>>>
> >>>> We could simply just name the structure, but I doubt this is the
> >>>> only place in the kernel code where it's being used this way :)
> >> This appears to be GCC bug #10676, see <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=10676>
> >> Says it was fixed in 4.6, but I believe the kernel supports GCCs much older
> >> than that (back to 3.2).  I personally hit it on 4.4.7, the version shipped
> >> with RHEL6.6.
> >
> > Yes, it will be fixed soon(ish).  Probably before you can get rid of the
> > obnoxious disclaimer... :)
> 
> It has been fixed by Andrew:
> 
> From: Andrew Morton <akpm@linux-foundation.org>
> Subject: arch/x86/kvm/mmu.c: work around gcc-4.4.4 bug

Folks, this fix is missing in both -tip and Linus' (4.1-rc7) tree. At
least I'm running into it.

Thanks,
Davidlohr

Re: [PATCH 1/2] KVM: MMU: fix SMAP virtualization

[Andrew Morton]

On Wed, 10 Jun 2015 11:02:46 -0700 Davidlohr Bueso <dave@stgolabs.net> wrote:

> On Wed, 2015-05-27 at 10:53 +0800, Xiao Guangrong wrote:
> > 
> > On 05/26/2015 10:48 PM, Paolo Bonzini wrote:
> > >
> > >
> > > On 26/05/2015 16:45, Edward Cree wrote:
> > >>>> This breaks older compilers that can't initialize anon structures.
> > >>>>
> > >>>> How old ? Even gcc 3.1 says you can use unnamed struct/union fields and
> > >>>> 3.2 is the minimum version required to compile the kernel as mentioned
> > >>>> in the README.
> > >>>>
> > >>>> We could simply just name the structure, but I doubt this is the
> > >>>> only place in the kernel code where it's being used this way :)
> > >> This appears to be GCC bug #10676, see <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=10676>
> > >> Says it was fixed in 4.6, but I believe the kernel supports GCCs much older
> > >> than that (back to 3.2).  I personally hit it on 4.4.7, the version shipped
> > >> with RHEL6.6.
> > >
> > > Yes, it will be fixed soon(ish).  Probably before you can get rid of the
> > > obnoxious disclaimer... :)
> > 
> > It has been fixed by Andrew:
> > 
> > From: Andrew Morton <akpm@linux-foundation.org>
> > Subject: arch/x86/kvm/mmu.c: work around gcc-4.4.4 bug
> 
> Folks, this fix is missing in both -tip and Linus' (4.1-rc7) tree. At
> least I'm running into it.

hm, yes, it's in linux-next so I dropped my copy.

I'll send it in to Linus today.

Re: [PATCH 1/2] KVM: MMU: fix SMAP virtualization

[Luis Henriques]

On Mon, Jun 08, 2015 at 10:14:49PM -0700, Vinson Lee wrote:
> On Tue, May 26, 2015 at 7:53 PM, Xiao Guangrong
> <guangrong.xiao@linux.intel.com> wrote:
> >
> >
> > On 05/26/2015 10:48 PM, Paolo Bonzini wrote:
> >>
> >>
> >>
> >> On 26/05/2015 16:45, Edward Cree wrote:
> >>>>>
> >>>>> This breaks older compilers that can't initialize anon structures.
> >>>>>
> >>>>> How old ? Even gcc 3.1 says you can use unnamed struct/union fields and
> >>>>> 3.2 is the minimum version required to compile the kernel as mentioned
> >>>>> in the README.
> >>>>>
> >>>>> We could simply just name the structure, but I doubt this is the
> >>>>> only place in the kernel code where it's being used this way :)
> >>>
> >>> This appears to be GCC bug #10676, see
> >>> <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=10676>
> >>> Says it was fixed in 4.6, but I believe the kernel supports GCCs much
> >>> older
> >>> than that (back to 3.2).  I personally hit it on 4.4.7, the version
> >>> shipped
> >>> with RHEL6.6.
> >>
> >>
> >> Yes, it will be fixed soon(ish).  Probably before you can get rid of the
> >> obnoxious disclaimer... :)
> >
> >
> > It has been fixed by Andrew:
> >
> > From: Andrew Morton <akpm@linux-foundation.org>
> > Subject: arch/x86/kvm/mmu.c: work around gcc-4.4.4 bug
> >
> > arch/x86/kvm/mmu.c: In function 'kvm_mmu_pte_write':
> > arch/x86/kvm/mmu.c:4256: error: unknown field 'cr0_wp' specified in
> > initializer
> > arch/x86/kvm/mmu.c:4257: error: unknown field 'cr4_pae' specified in
> > initializer
> > arch/x86/kvm/mmu.c:4257: warning: excess elements in union initializer
> > ...
> >
> > gcc-4.4.4 (at least) has issues when using anonymous unions in
> > initializers.
> >
> > Fixes: edc90b7dc4ceef6 ("KVM: MMU: fix SMAP virtualization")
> > Cc: Xiao Guangrong <guangrong.xiao@linux.intel.com>
> > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> >
> > Should be found at -mm tree.
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at  http://www.tux.org/lkml/
> 
> Hi.
> 
> Please backport "arch/x86/kvm/mmu.c: work around gcc-4.4.4 bug" to
> stable trees that have backported "KVM: MMU: fix SMAP virtualization".
> 
> Currently, the Linux 4.0.5 build is broken with GCC 4.4.
> 
> "KVM: MMU: fix SMAP virtualization" is currently queued for 3.16.y-ckt
> and 3.18.y.
> 
> Cheers,
> Vinson
> --
> To unsubscribe from this list: send the line "unsubscribe stable" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

I believe you're referring to the following commit:

commit 5ec45a192fe6e287f0fc06d5ca4f3bd446d94803
Author: Andrew Morton <akpm@linux-foundation.org>
Date:   Wed Jun 10 11:15:02 2015 -0700

    arch/x86/kvm/mmu.c: work around gcc-4.4.4 bug

I am queuing it for the 3.16 kernel.  Thanks!

Cheers,
--
Luís

Re: [PATCH 1/2] KVM: MMU: fix SMAP virtualization

[Luis Henriques]

On Mon, Jun 08, 2015 at 10:14:49PM -0700, Vinson Lee wrote:
> On Tue, May 26, 2015 at 7:53 PM, Xiao Guangrong
> <guangrong.xiao@linux.intel.com> wrote:
> >
> >
> > On 05/26/2015 10:48 PM, Paolo Bonzini wrote:
> >>
> >>
> >>
> >> On 26/05/2015 16:45, Edward Cree wrote:
> >>>>>
> >>>>> This breaks older compilers that can't initialize anon structures.
> >>>>>
> >>>>> How old ? Even gcc 3.1 says you can use unnamed struct/union fields and
> >>>>> 3.2 is the minimum version required to compile the kernel as mentioned
> >>>>> in the README.
> >>>>>
> >>>>> We could simply just name the structure, but I doubt this is the
> >>>>> only place in the kernel code where it's being used this way :)
> >>>
> >>> This appears to be GCC bug #10676, see
> >>> <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=10676>
> >>> Says it was fixed in 4.6, but I believe the kernel supports GCCs much
> >>> older
> >>> than that (back to 3.2).  I personally hit it on 4.4.7, the version
> >>> shipped
> >>> with RHEL6.6.
> >>
> >>
> >> Yes, it will be fixed soon(ish).  Probably before you can get rid of the
> >> obnoxious disclaimer... :)
> >
> >
> > It has been fixed by Andrew:
> >
> > From: Andrew Morton <akpm@linux-foundation.org>
> > Subject: arch/x86/kvm/mmu.c: work around gcc-4.4.4 bug
> >
> > arch/x86/kvm/mmu.c: In function 'kvm_mmu_pte_write':
> > arch/x86/kvm/mmu.c:4256: error: unknown field 'cr0_wp' specified in
> > initializer
> > arch/x86/kvm/mmu.c:4257: error: unknown field 'cr4_pae' specified in
> > initializer
> > arch/x86/kvm/mmu.c:4257: warning: excess elements in union initializer
> > ...
> >
> > gcc-4.4.4 (at least) has issues when using anonymous unions in
> > initializers.
> >
> > Fixes: edc90b7dc4ceef6 ("KVM: MMU: fix SMAP virtualization")
> > Cc: Xiao Guangrong <guangrong.xiao@linux.intel.com>
> > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> >
> > Should be found at -mm tree.
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at  http://www.tux.org/lkml/
> 
> Hi.
> 
> Please backport "arch/x86/kvm/mmu.c: work around gcc-4.4.4 bug" to
> stable trees that have backported "KVM: MMU: fix SMAP virtualization".
> 
> Currently, the Linux 4.0.5 build is broken with GCC 4.4.
> 
> "KVM: MMU: fix SMAP virtualization" is currently queued for 3.16.y-ckt
> and 3.18.y.
> 
> Cheers,
> Vinson
> --
> To unsubscribe from this list: send the line "unsubscribe stable" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

I believe you're referring to the following commit:

commit 5ec45a192fe6e287f0fc06d5ca4f3bd446d94803
Author: Andrew Morton <akpm@linux-foundation.org>
Date:   Wed Jun 10 11:15:02 2015 -0700

    arch/x86/kvm/mmu.c: work around gcc-4.4.4 bug

I am queuing it for the 3.16 kernel.  Thanks!

Cheers,
--
Lu�s