[PATCH] KVM: arm64/sve: Fix vq_present() macro to yield a bool

[PATCH] KVM: arm64/sve: Fix vq_present() macro to yield a bool

[Dave Martin]

From: Zhang Lei <zhang.lei@jp.fujitsu.com>

The original implementation of vq_present() relied on aggressive
inlining in order for the compiler to know that the code is
correct, due to some const-casting issues.  This was causing sparse
and clang to complain, while GCC compiled cleanly.

Commit 0c529ff789bc addressed this problem, but since vq_present()
is no longer a function, there is now no implicit casting of the
returned value to the return type (bool).

In set_sve_vls(), this uncast bit value is compared against a bool,
and so may spuriously compare as unequal when both are nonzero.  As
a result, KVM may reject valid SVE vector length configurations as
invalid, and vice versa.

Fix it by forcing the returned value to a bool.

Signed-off-by: Zhang Lei <zhang.lei@jp.fujitsu.com>
Fixes: 0c529ff789bc ("KVM: arm64: Implement vq_present() as a macro")
Signed-off-by: Dave Martin <Dave.Martin@arm.com> [commit message rewrite]
Cc: Viresh Kumar <viresh.kumar@linaro.org>

---

Posting this under Zhang Lei's authorship, due to the need to turn this
fix around quickly.  The fix is as per the original suggestion [1].

Originally observed with the QEMU KVM SVE support under review:
https://lists.gnu.org/archive/html/qemu-devel/2019-06/msg04945.html

Bug reproduced and fix tested on the Arm Fast Model, with
http://linux-arm.org/git?p=kvmtool-dm.git;a=shortlog;h=refs/heads/sve/v3/head
(After rerunning util/update_headers.sh.)

(the --sve-vls command line argument was removed in v4 of the
kvmtool patches).

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2019-July/664633.html
---
 arch/arm64/kvm/guest.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
index c2afa79..dfd6264 100644
--- a/arch/arm64/kvm/guest.c
+++ b/arch/arm64/kvm/guest.c
@@ -208,7 +208,7 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
 
 #define vq_word(vq) (((vq) - SVE_VQ_MIN) / 64)
 #define vq_mask(vq) ((u64)1 << ((vq) - SVE_VQ_MIN) % 64)
-#define vq_present(vqs, vq) ((vqs)[vq_word(vq)] & vq_mask(vq))
+#define vq_present(vqs, vq) (!!((vqs)[vq_word(vq)] & vq_mask(vq)))
 
 static int get_sve_vls(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
 {
-- 
2.1.4

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Re: [PATCH] KVM: arm64/sve: Fix vq_present() macro to yield a bool

[Viresh Kumar]

On 03-07-19, 18:42, Dave Martin wrote:
> From: Zhang Lei <zhang.lei@jp.fujitsu.com>
> 
> The original implementation of vq_present() relied on aggressive
> inlining in order for the compiler to know that the code is
> correct, due to some const-casting issues.  This was causing sparse
> and clang to complain, while GCC compiled cleanly.
> 
> Commit 0c529ff789bc addressed this problem, but since vq_present()
> is no longer a function, there is now no implicit casting of the
> returned value to the return type (bool).
> 
> In set_sve_vls(), this uncast bit value is compared against a bool,
> and so may spuriously compare as unequal when both are nonzero.  As
> a result, KVM may reject valid SVE vector length configurations as
> invalid, and vice versa.
> 
> Fix it by forcing the returned value to a bool.
> 
> Signed-off-by: Zhang Lei <zhang.lei@jp.fujitsu.com>
> Fixes: 0c529ff789bc ("KVM: arm64: Implement vq_present() as a macro")
> Signed-off-by: Dave Martin <Dave.Martin@arm.com> [commit message rewrite]
> Cc: Viresh Kumar <viresh.kumar@linaro.org>
> 
> ---
> 
> Posting this under Zhang Lei's authorship, due to the need to turn this
> fix around quickly.  The fix is as per the original suggestion [1].
> 
> Originally observed with the QEMU KVM SVE support under review:
> https://lists.gnu.org/archive/html/qemu-devel/2019-06/msg04945.html
> 
> Bug reproduced and fix tested on the Arm Fast Model, with
> http://linux-arm.org/git?p=kvmtool-dm.git;a=shortlog;h=refs/heads/sve/v3/head
> (After rerunning util/update_headers.sh.)
> 
> (the --sve-vls command line argument was removed in v4 of the
> kvmtool patches).
> 
> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2019-July/664633.html
> ---
>  arch/arm64/kvm/guest.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index c2afa79..dfd6264 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -208,7 +208,7 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>  
>  #define vq_word(vq) (((vq) - SVE_VQ_MIN) / 64)
>  #define vq_mask(vq) ((u64)1 << ((vq) - SVE_VQ_MIN) % 64)
> -#define vq_present(vqs, vq) ((vqs)[vq_word(vq)] & vq_mask(vq))
> +#define vq_present(vqs, vq) (!!((vqs)[vq_word(vq)] & vq_mask(vq)))
>  
>  static int get_sve_vls(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>  {

It was a really nice bug :)

Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>

-- 
viresh
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Re: [PATCH] KVM: arm64/sve: Fix vq_present() macro to yield a bool

[Dave Martin]

On Thu, Jul 04, 2019 at 08:32:52AM +0530, Viresh Kumar wrote:
> On 03-07-19, 18:42, Dave Martin wrote:
> > From: Zhang Lei <zhang.lei@jp.fujitsu.com>
> > 
> > The original implementation of vq_present() relied on aggressive
> > inlining in order for the compiler to know that the code is
> > correct, due to some const-casting issues.  This was causing sparse
> > and clang to complain, while GCC compiled cleanly.
> > 
> > Commit 0c529ff789bc addressed this problem, but since vq_present()
> > is no longer a function, there is now no implicit casting of the
> > returned value to the return type (bool).
> > 
> > In set_sve_vls(), this uncast bit value is compared against a bool,
> > and so may spuriously compare as unequal when both are nonzero.  As
> > a result, KVM may reject valid SVE vector length configurations as
> > invalid, and vice versa.
> > 
> > Fix it by forcing the returned value to a bool.
> > 
> > Signed-off-by: Zhang Lei <zhang.lei@jp.fujitsu.com>
> > Fixes: 0c529ff789bc ("KVM: arm64: Implement vq_present() as a macro")
> > Signed-off-by: Dave Martin <Dave.Martin@arm.com> [commit message rewrite]
> > Cc: Viresh Kumar <viresh.kumar@linaro.org>
> > 
> > ---
> > 
> > Posting this under Zhang Lei's authorship, due to the need to turn this
> > fix around quickly.  The fix is as per the original suggestion [1].
> > 
> > Originally observed with the QEMU KVM SVE support under review:
> > https://lists.gnu.org/archive/html/qemu-devel/2019-06/msg04945.html
> > 
> > Bug reproduced and fix tested on the Arm Fast Model, with
> > http://linux-arm.org/git?p=kvmtool-dm.git;a=shortlog;h=refs/heads/sve/v3/head
> > (After rerunning util/update_headers.sh.)
> > 
> > (the --sve-vls command line argument was removed in v4 of the
> > kvmtool patches).
> > 
> > [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2019-July/664633.html
> > ---
> >  arch/arm64/kvm/guest.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> > index c2afa79..dfd6264 100644
> > --- a/arch/arm64/kvm/guest.c
> > +++ b/arch/arm64/kvm/guest.c
> > @@ -208,7 +208,7 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> >  
> >  #define vq_word(vq) (((vq) - SVE_VQ_MIN) / 64)
> >  #define vq_mask(vq) ((u64)1 << ((vq) - SVE_VQ_MIN) % 64)
> > -#define vq_present(vqs, vq) ((vqs)[vq_word(vq)] & vq_mask(vq))
> > +#define vq_present(vqs, vq) (!!((vqs)[vq_word(vq)] & vq_mask(vq)))
> >  
> >  static int get_sve_vls(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> >  {
> 
> It was a really nice bug :)
> 
> Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>

Thanks for the quick review!

Maybe it makes sense to write equality comparisons on bools as !x == !y
to be more defensive against this kind of thing.  Anyway, probably best
to leave this as-is while the dust settles.

Cheers
---Dave
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RE: [PATCH] KVM: arm64/sve: Fix vq_present() macro to yield a bool

[Zhang, Lei]

Hi guys,

I have started up KVM guest os successfully with SVE feature with Dave' patch.

Tested-by: Zhang Lei <zhang.lei@jp.fujitsu.com >

> -----Original Message-----
> From: Dave Martin <Dave.Martin@arm.com>
> Sent: Thursday, July 04, 2019 5:35 PM
> To: Viresh Kumar <viresh.kumar@linaro.org>
> Cc: Okamoto, Takayuki/岡本 高幸 <tokamoto@jp.fujitsu.com>; Christoffer
> Dall <cdall@kernel.org>; Ard Biesheuvel <ard.biesheuvel@linaro.org>; Marc
> Zyngier <marc.zyngier@arm.com>; Catalin Marinas
> <catalin.marinas@arm.com>; Will Deacon <will.deacon@arm.com>; Zhang,
> Lei/張 雷 <zhang.lei@jp.fujitsu.com>; Julien Grall <julien.grall@arm.com>;
> kvmarm@lists.cs.columbia.edu; linux-arm-kernel@lists.infradead.org
> Subject: Re: [PATCH] KVM: arm64/sve: Fix vq_present() macro to yield a bool
> 
> On Thu, Jul 04, 2019 at 08:32:52AM +0530, Viresh Kumar wrote:
> > On 03-07-19, 18:42, Dave Martin wrote:
> > > From: Zhang Lei <zhang.lei@jp.fujitsu.com>
> > >
> > > The original implementation of vq_present() relied on aggressive
> > > inlining in order for the compiler to know that the code is correct,
> > > due to some const-casting issues.  This was causing sparse and clang
> > > to complain, while GCC compiled cleanly.
> > >
> > > Commit 0c529ff789bc addressed this problem, but since vq_present()
> > > is no longer a function, there is now no implicit casting of the
> > > returned value to the return type (bool).
> > >
> > > In set_sve_vls(), this uncast bit value is compared against a bool,
> > > and so may spuriously compare as unequal when both are nonzero.  As
> > > a result, KVM may reject valid SVE vector length configurations as
> > > invalid, and vice versa.
> > >
> > > Fix it by forcing the returned value to a bool.
> > >
> > > Signed-off-by: Zhang Lei <zhang.lei@jp.fujitsu.com>
> > > Fixes: 0c529ff789bc ("KVM: arm64: Implement vq_present() as a
> > > macro")
> > > Signed-off-by: Dave Martin <Dave.Martin@arm.com> [commit message
> > > rewrite]
> > > Cc: Viresh Kumar <viresh.kumar@linaro.org>
> > >
> > > ---
> > >
> > > Posting this under Zhang Lei's authorship, due to the need to turn
> > > this fix around quickly.  The fix is as per the original suggestion [1].
> > >
> > > Originally observed with the QEMU KVM SVE support under review:
> > > https://lists.gnu.org/archive/html/qemu-devel/2019-06/msg04945.html
> > >
> > > Bug reproduced and fix tested on the Arm Fast Model, with
> > > http://linux-arm.org/git?p=kvmtool-dm.git;a=shortlog;h=refs/heads/sv
> > > e/v3/head (After rerunning util/update_headers.sh.)
> > >
> > > (the --sve-vls command line argument was removed in v4 of the
> > > kvmtool patches).
> > >
> > > [1]
> > > http://lists.infradead.org/pipermail/linux-arm-kernel/2019-July/6646
> > > 33.html
> > > ---
> > >  arch/arm64/kvm/guest.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c index
> > > c2afa79..dfd6264 100644
> > > --- a/arch/arm64/kvm/guest.c
> > > +++ b/arch/arm64/kvm/guest.c
> > > @@ -208,7 +208,7 @@ static int set_core_reg(struct kvm_vcpu *vcpu,
> > > const struct kvm_one_reg *reg)
> > >
> > >  #define vq_word(vq) (((vq) - SVE_VQ_MIN) / 64)  #define vq_mask(vq)
> > > ((u64)1 << ((vq) - SVE_VQ_MIN) % 64) -#define vq_present(vqs, vq)
> > > ((vqs)[vq_word(vq)] & vq_mask(vq))
> > > +#define vq_present(vqs, vq) (!!((vqs)[vq_word(vq)] & vq_mask(vq)))
> > >
> > >  static int get_sve_vls(struct kvm_vcpu *vcpu, const struct
> > > kvm_one_reg *reg)  {
> >
> > It was a really nice bug :)
> >
> > Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
> 
> Thanks for the quick review!
> 
> Maybe it makes sense to write equality comparisons on bools as !x == !y to be
> more defensive against this kind of thing.  Anyway, probably best to leave this
> as-is while the dust settles.
> 
> Cheers
> ---Dave
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Re: [PATCH] KVM: arm64/sve: Fix vq_present() macro to yield a bool

[Dave Martin]

On Thu, Jul 04, 2019 at 10:04:08AM +0000, Zhang, Lei wrote:
> Hi guys,
> 
> I have started up KVM guest os successfully with SVE feature with Dave' patch.
> 
> Tested-by: Zhang Lei <zhang.lei@jp.fujitsu.com >

Thanks for verifying.

It's really your fix, I only wrote a commit message for it :)

[...]

Cheers
---Dave
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Re: [PATCH] KVM: arm64/sve: Fix vq_present() macro to yield a bool

[Marc Zyngier]

+KVM, Paolo and Radim,

Guys, do you mind picking this single patch and sending it to Linus?
That's the only fix left for 5.2. Alternatively, I can send you a pull
request, but it feels overkill.

Either way, please let me know.

Thanks,

	M.

On Wed, 03 Jul 2019 18:42:50 +0100,
Dave Martin <Dave.Martin@arm.com> wrote:
> 
> From: Zhang Lei <zhang.lei@jp.fujitsu.com>
> 
> The original implementation of vq_present() relied on aggressive
> inlining in order for the compiler to know that the code is
> correct, due to some const-casting issues.  This was causing sparse
> and clang to complain, while GCC compiled cleanly.
> 
> Commit 0c529ff789bc addressed this problem, but since vq_present()
> is no longer a function, there is now no implicit casting of the
> returned value to the return type (bool).
> 
> In set_sve_vls(), this uncast bit value is compared against a bool,
> and so may spuriously compare as unequal when both are nonzero.  As
> a result, KVM may reject valid SVE vector length configurations as
> invalid, and vice versa.
> 
> Fix it by forcing the returned value to a bool.
> 
> Signed-off-by: Zhang Lei <zhang.lei@jp.fujitsu.com>
> Fixes: 0c529ff789bc ("KVM: arm64: Implement vq_present() as a macro")
> Signed-off-by: Dave Martin <Dave.Martin@arm.com> [commit message rewrite]
> Cc: Viresh Kumar <viresh.kumar@linaro.org>
> 
> ---
> 
> Posting this under Zhang Lei's authorship, due to the need to turn this
> fix around quickly.  The fix is as per the original suggestion [1].
> 
> Originally observed with the QEMU KVM SVE support under review:
> https://lists.gnu.org/archive/html/qemu-devel/2019-06/msg04945.html
> 
> Bug reproduced and fix tested on the Arm Fast Model, with
> http://linux-arm.org/git?p=kvmtool-dm.git;a=shortlog;h=refs/heads/sve/v3/head
> (After rerunning util/update_headers.sh.)
> 
> (the --sve-vls command line argument was removed in v4 of the
> kvmtool patches).
> 
> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2019-July/664633.html
> ---
>  arch/arm64/kvm/guest.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index c2afa79..dfd6264 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -208,7 +208,7 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>  
>  #define vq_word(vq) (((vq) - SVE_VQ_MIN) / 64)
>  #define vq_mask(vq) ((u64)1 << ((vq) - SVE_VQ_MIN) % 64)
> -#define vq_present(vqs, vq) ((vqs)[vq_word(vq)] & vq_mask(vq))
> +#define vq_present(vqs, vq) (!!((vqs)[vq_word(vq)] & vq_mask(vq)))
>  
>  static int get_sve_vls(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>  {
> -- 
> 2.1.4
> 

-- 
Jazz is not dead, it just smells funny.
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Re: [PATCH] KVM: arm64/sve: Fix vq_present() macro to yield a bool

[Paolo Bonzini]

On 04/07/19 10:20, Marc Zyngier wrote:
> +KVM, Paolo and Radim,
> 
> Guys, do you mind picking this single patch and sending it to Linus?
> That's the only fix left for 5.2. Alternatively, I can send you a pull
> request, but it feels overkill.

Sure, will do.

Paolo

> Either way, please let me know.
> 
> Thanks,
> 
> 	M.
> 
> On Wed, 03 Jul 2019 18:42:50 +0100,
> Dave Martin <Dave.Martin@arm.com> wrote:
>>
>> From: Zhang Lei <zhang.lei@jp.fujitsu.com>
>>
>> The original implementation of vq_present() relied on aggressive
>> inlining in order for the compiler to know that the code is
>> correct, due to some const-casting issues.  This was causing sparse
>> and clang to complain, while GCC compiled cleanly.
>>
>> Commit 0c529ff789bc addressed this problem, but since vq_present()
>> is no longer a function, there is now no implicit casting of the
>> returned value to the return type (bool).
>>
>> In set_sve_vls(), this uncast bit value is compared against a bool,
>> and so may spuriously compare as unequal when both are nonzero.  As
>> a result, KVM may reject valid SVE vector length configurations as
>> invalid, and vice versa.
>>
>> Fix it by forcing the returned value to a bool.
>>
>> Signed-off-by: Zhang Lei <zhang.lei@jp.fujitsu.com>
>> Fixes: 0c529ff789bc ("KVM: arm64: Implement vq_present() as a macro")
>> Signed-off-by: Dave Martin <Dave.Martin@arm.com> [commit message rewrite]
>> Cc: Viresh Kumar <viresh.kumar@linaro.org>
>>
>> ---
>>
>> Posting this under Zhang Lei's authorship, due to the need to turn this
>> fix around quickly.  The fix is as per the original suggestion [1].
>>
>> Originally observed with the QEMU KVM SVE support under review:
>> https://lists.gnu.org/archive/html/qemu-devel/2019-06/msg04945.html
>>
>> Bug reproduced and fix tested on the Arm Fast Model, with
>> http://linux-arm.org/git?p=kvmtool-dm.git;a=shortlog;h=refs/heads/sve/v3/head
>> (After rerunning util/update_headers.sh.)
>>
>> (the --sve-vls command line argument was removed in v4 of the
>> kvmtool patches).
>>
>> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2019-July/664633.html
>> ---
>>  arch/arm64/kvm/guest.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
>> index c2afa79..dfd6264 100644
>> --- a/arch/arm64/kvm/guest.c
>> +++ b/arch/arm64/kvm/guest.c
>> @@ -208,7 +208,7 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>>  
>>  #define vq_word(vq) (((vq) - SVE_VQ_MIN) / 64)
>>  #define vq_mask(vq) ((u64)1 << ((vq) - SVE_VQ_MIN) % 64)
>> -#define vq_present(vqs, vq) ((vqs)[vq_word(vq)] & vq_mask(vq))
>> +#define vq_present(vqs, vq) (!!((vqs)[vq_word(vq)] & vq_mask(vq)))
>>  
>>  static int get_sve_vls(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>>  {
>> -- 
>> 2.1.4
>>
> 

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Re: [PATCH] KVM: arm64/sve: Fix vq_present() macro to yield a bool

[Dave Martin]

On Thu, Jul 04, 2019 at 02:24:42PM +0200, Paolo Bonzini wrote:
> On 04/07/19 10:20, Marc Zyngier wrote:
> > +KVM, Paolo and Radim,
> > 
> > Guys, do you mind picking this single patch and sending it to Linus?
> > That's the only fix left for 5.2. Alternatively, I can send you a pull
> > request, but it feels overkill.
> 
> Sure, will do.
> 
> Paolo

Thanks all for the quick turnaround!

[...]

Cheers
---Dave
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