Re: [PATCH 1/8] ppc/kvm: Replace ACCESS_ONCE with READ_ONCE
Am 16.01.2015 um 00:09 schrieb Michael Ellerman:
> On Thu, 2015-01-15 at 09:58 +0100, Christian Borntraeger wrote:
>> ACCESS_ONCE does not work reliably on non-scalar types. For
>> example gcc 4.6 and 4.7 might remove the volatile tag for such
>> accesses during the SRA (scalar replacement of aggregates) step
>> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145)
>>
>> Change the ppc/kvm code to replace ACCESS_ONCE with READ_ONCE.
>>
>> Signed-off-by: Christian Borntraeger
>> ---
>> arch/powerpc/kvm/book3s_hv_rm_xics.c | 8
>> arch/powerpc/kvm/book3s_xics.c | 16
>> 2 files changed, 12 insertions(+), 12 deletions(-)
>>
>> diff --git a/arch/powerpc/kvm/book3s_hv_rm_xics.c
>> b/arch/powerpc/kvm/book3s_hv_rm_xics.c
>> index 7b066f6..7c22997 100644
>> --- a/arch/powerpc/kvm/book3s_hv_rm_xics.c
>> +++ b/arch/powerpc/kvm/book3s_hv_rm_xics.c
>> @@ -152,7 +152,7 @@ static void icp_rm_down_cppr(struct kvmppc_xics *xics,
>> struct kvmppc_icp *icp,
>> * in virtual mode.
>> */
>> do {
>> -old_state = new_state = ACCESS_ONCE(icp->state);
>> +old_state = new_state = READ_ONCE(icp->state);
>
> These are all icp->state.
>
> Which is a union, but it's only the size of unsigned long. So in practice
> there
> shouldn't be a bug here right?
This bug was that gcc lost the volatile tag when propagating aggregates to
scalar types.
So in theory a union could be affected. See the original problem
( http://marc.info/?i=54611D86.4040306%40de.ibm.com )
which happened on
union ipte_control {
unsigned long val;
struct {
unsigned long k : 1;
unsigned long kh : 31;
unsigned long kg : 32;
};
};
Christian
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/8] ppc/kvm: Replace ACCESS_ONCE with READ_ONCE
Am 16.01.2015 um 00:09 schrieb Michael Ellerman:
On Thu, 2015-01-15 at 09:58 +0100, Christian Borntraeger wrote:
ACCESS_ONCE does not work reliably on non-scalar types. For
example gcc 4.6 and 4.7 might remove the volatile tag for such
accesses during the SRA (scalar replacement of aggregates) step
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145)
Change the ppc/kvm code to replace ACCESS_ONCE with READ_ONCE.
Signed-off-by: Christian Borntraeger borntrae...@de.ibm.com
---
arch/powerpc/kvm/book3s_hv_rm_xics.c | 8
arch/powerpc/kvm/book3s_xics.c | 16
2 files changed, 12 insertions(+), 12 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_hv_rm_xics.c
b/arch/powerpc/kvm/book3s_hv_rm_xics.c
index 7b066f6..7c22997 100644
--- a/arch/powerpc/kvm/book3s_hv_rm_xics.c
+++ b/arch/powerpc/kvm/book3s_hv_rm_xics.c
@@ -152,7 +152,7 @@ static void icp_rm_down_cppr(struct kvmppc_xics *xics,
struct kvmppc_icp *icp,
* in virtual mode.
*/
do {
-old_state = new_state = ACCESS_ONCE(icp-state);
+old_state = new_state = READ_ONCE(icp-state);
These are all icp-state.
Which is a union, but it's only the size of unsigned long. So in practice
there
shouldn't be a bug here right?
This bug was that gcc lost the volatile tag when propagating aggregates to
scalar types.
So in theory a union could be affected. See the original problem
( http://marc.info/?i=54611D86.4040306%40de.ibm.com )
which happened on
union ipte_control {
unsigned long val;
struct {
unsigned long k : 1;
unsigned long kh : 31;
unsigned long kg : 32;
};
};
Christian
--
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/8] ppc/kvm: Replace ACCESS_ONCE with READ_ONCE
On Thu, 2015-01-15 at 09:58 +0100, Christian Borntraeger wrote:
> ACCESS_ONCE does not work reliably on non-scalar types. For
> example gcc 4.6 and 4.7 might remove the volatile tag for such
> accesses during the SRA (scalar replacement of aggregates) step
> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145)
>
> Change the ppc/kvm code to replace ACCESS_ONCE with READ_ONCE.
>
> Signed-off-by: Christian Borntraeger
> ---
> arch/powerpc/kvm/book3s_hv_rm_xics.c | 8
> arch/powerpc/kvm/book3s_xics.c | 16
> 2 files changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv_rm_xics.c
> b/arch/powerpc/kvm/book3s_hv_rm_xics.c
> index 7b066f6..7c22997 100644
> --- a/arch/powerpc/kvm/book3s_hv_rm_xics.c
> +++ b/arch/powerpc/kvm/book3s_hv_rm_xics.c
> @@ -152,7 +152,7 @@ static void icp_rm_down_cppr(struct kvmppc_xics *xics,
> struct kvmppc_icp *icp,
>* in virtual mode.
>*/
> do {
> - old_state = new_state = ACCESS_ONCE(icp->state);
> + old_state = new_state = READ_ONCE(icp->state);
These are all icp->state.
Which is a union, but it's only the size of unsigned long. So in practice there
shouldn't be a bug here right?
cheers
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/8] ppc/kvm: Replace ACCESS_ONCE with READ_ONCE
On Thu, 2015-01-15 at 09:58 +0100, Christian Borntraeger wrote:
ACCESS_ONCE does not work reliably on non-scalar types. For
example gcc 4.6 and 4.7 might remove the volatile tag for such
accesses during the SRA (scalar replacement of aggregates) step
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145)
Change the ppc/kvm code to replace ACCESS_ONCE with READ_ONCE.
Signed-off-by: Christian Borntraeger borntrae...@de.ibm.com
---
arch/powerpc/kvm/book3s_hv_rm_xics.c | 8
arch/powerpc/kvm/book3s_xics.c | 16
2 files changed, 12 insertions(+), 12 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_hv_rm_xics.c
b/arch/powerpc/kvm/book3s_hv_rm_xics.c
index 7b066f6..7c22997 100644
--- a/arch/powerpc/kvm/book3s_hv_rm_xics.c
+++ b/arch/powerpc/kvm/book3s_hv_rm_xics.c
@@ -152,7 +152,7 @@ static void icp_rm_down_cppr(struct kvmppc_xics *xics,
struct kvmppc_icp *icp,
* in virtual mode.
*/
do {
- old_state = new_state = ACCESS_ONCE(icp-state);
+ old_state = new_state = READ_ONCE(icp-state);
These are all icp-state.
Which is a union, but it's only the size of unsigned long. So in practice there
shouldn't be a bug here right?
cheers
--
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
