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* [PATCHv2 1/2] hwrng: optee: handle unlimited data rates
@ 2020-07-23  8:46 Jorge Ramirez-Ortiz
  2020-07-23  8:46 ` [PATCHv2 2/2] hwrng: optee: fix wait use case Jorge Ramirez-Ortiz
  2020-07-24 13:24 ` [PATCHv2 1/2] hwrng: optee: handle unlimited data rates Sumit Garg
  0 siblings, 2 replies; 14+ messages in thread
From: Jorge Ramirez-Ortiz @ 2020-07-23  8:46 UTC (permalink / raw)
  To: jorge, sumit.garg, mpm, herbert
  Cc: jens.wiklander, arnd, ricardo, mike, gregkh, op-tee,
	linux-crypto, linux-kernel

Data rates of MAX_UINT32 will schedule an unnecessary one jiffy
timeout on the call to msleep. Avoid this scenario by using 0 as the
unlimited data rate.

Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
---
 drivers/char/hw_random/optee-rng.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
index 49b2e02537dd..5bc4700c4dae 100644
--- a/drivers/char/hw_random/optee-rng.c
+++ b/drivers/char/hw_random/optee-rng.c
@@ -128,7 +128,7 @@ static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
 		data += rng_size;
 		read += rng_size;
 
-		if (wait) {
+		if (wait && pvt_data->data_rate) {
 			if (timeout-- == 0)
 				return read;
 			msleep((1000 * (max - read)) / pvt_data->data_rate);
-- 
2.17.1


^ permalink raw reply	[flat|nested] 14+ messages in thread

* [PATCHv2 2/2] hwrng: optee: fix wait use case
  2020-07-23  8:46 [PATCHv2 1/2] hwrng: optee: handle unlimited data rates Jorge Ramirez-Ortiz
@ 2020-07-23  8:46 ` Jorge Ramirez-Ortiz
  2020-07-24 13:22   ` Sumit Garg
  2020-08-05 13:34   ` Jorge Ramirez-Ortiz, Foundries
  2020-07-24 13:24 ` [PATCHv2 1/2] hwrng: optee: handle unlimited data rates Sumit Garg
  1 sibling, 2 replies; 14+ messages in thread
From: Jorge Ramirez-Ortiz @ 2020-07-23  8:46 UTC (permalink / raw)
  To: jorge, sumit.garg, mpm, herbert
  Cc: jens.wiklander, arnd, ricardo, mike, gregkh, op-tee,
	linux-crypto, linux-kernel

The current code waits for data to be available before attempting a
second read. However the second read would not be executed as the
while loop exits.

This fix does not wait if all data has been read and reads a second
time if only partial data was retrieved on the first read.

This fix also does not attempt to read if not data is requested.

Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
---
 v2: tidy up the while loop to avoid reading when no data is requested

 drivers/char/hw_random/optee-rng.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
index 5bc4700c4dae..a99d82949981 100644
--- a/drivers/char/hw_random/optee-rng.c
+++ b/drivers/char/hw_random/optee-rng.c
@@ -122,14 +122,14 @@ static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
 	if (max > MAX_ENTROPY_REQ_SZ)
 		max = MAX_ENTROPY_REQ_SZ;
 
-	while (read == 0) {
+	while (read < max) {
 		rng_size = get_optee_rng_data(pvt_data, data, (max - read));
 
 		data += rng_size;
 		read += rng_size;
 
 		if (wait && pvt_data->data_rate) {
-			if (timeout-- == 0)
+			if ((timeout-- == 0) || (read == max))
 				return read;
 			msleep((1000 * (max - read)) / pvt_data->data_rate);
 		} else {
-- 
2.17.1


^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCHv2 2/2] hwrng: optee: fix wait use case
  2020-07-23  8:46 ` [PATCHv2 2/2] hwrng: optee: fix wait use case Jorge Ramirez-Ortiz
@ 2020-07-24 13:22   ` Sumit Garg
  2020-07-24 14:23     ` Jorge Ramirez-Ortiz, Foundries
  2020-08-05 13:34   ` Jorge Ramirez-Ortiz, Foundries
  1 sibling, 1 reply; 14+ messages in thread
From: Sumit Garg @ 2020-07-24 13:22 UTC (permalink / raw)
  To: Jorge Ramirez-Ortiz
  Cc: Matt Mackall, Herbert Xu, Jens Wiklander, Arnd Bergmann, ricardo,
	Michael Scott, Greg Kroah-Hartman, op-tee,
	open list:HARDWARE RANDOM NUMBER GENERATOR CORE,
	Linux Kernel Mailing List

On Thu, 23 Jul 2020 at 14:16, Jorge Ramirez-Ortiz <jorge@foundries.io> wrote:
>
> The current code waits for data to be available before attempting a
> second read. However the second read would not be executed as the
> while loop exits.
>
> This fix does not wait if all data has been read and reads a second
> time if only partial data was retrieved on the first read.
>
> This fix also does not attempt to read if not data is requested.

I am not sure how this is possible, can you elaborate?

>
> Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
> ---
>  v2: tidy up the while loop to avoid reading when no data is requested
>
>  drivers/char/hw_random/optee-rng.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
> index 5bc4700c4dae..a99d82949981 100644
> --- a/drivers/char/hw_random/optee-rng.c
> +++ b/drivers/char/hw_random/optee-rng.c
> @@ -122,14 +122,14 @@ static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
>         if (max > MAX_ENTROPY_REQ_SZ)
>                 max = MAX_ENTROPY_REQ_SZ;
>
> -       while (read == 0) {
> +       while (read < max) {
>                 rng_size = get_optee_rng_data(pvt_data, data, (max - read));
>
>                 data += rng_size;
>                 read += rng_size;
>
>                 if (wait && pvt_data->data_rate) {
> -                       if (timeout-- == 0)
> +                       if ((timeout-- == 0) || (read == max))

If read == max, would there be any sleep?

-Sumit

>                                 return read;
>                         msleep((1000 * (max - read)) / pvt_data->data_rate);
>                 } else {
> --
> 2.17.1
>

^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCHv2 1/2] hwrng: optee: handle unlimited data rates
  2020-07-23  8:46 [PATCHv2 1/2] hwrng: optee: handle unlimited data rates Jorge Ramirez-Ortiz
  2020-07-23  8:46 ` [PATCHv2 2/2] hwrng: optee: fix wait use case Jorge Ramirez-Ortiz
@ 2020-07-24 13:24 ` Sumit Garg
  1 sibling, 0 replies; 14+ messages in thread
From: Sumit Garg @ 2020-07-24 13:24 UTC (permalink / raw)
  To: Jorge Ramirez-Ortiz
  Cc: Matt Mackall, Herbert Xu, Jens Wiklander, Arnd Bergmann, ricardo,
	Michael Scott, Greg Kroah-Hartman, op-tee,
	open list:HARDWARE RANDOM NUMBER GENERATOR CORE,
	Linux Kernel Mailing List

On Thu, 23 Jul 2020 at 14:16, Jorge Ramirez-Ortiz <jorge@foundries.io> wrote:
>
> Data rates of MAX_UINT32 will schedule an unnecessary one jiffy
> timeout on the call to msleep. Avoid this scenario by using 0 as the
> unlimited data rate.
>
> Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
> ---
>  drivers/char/hw_random/optee-rng.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>

Sounds good to me. FWIW:

Reviewed-by: Sumit Garg <sumit.garg@linaro.org>

-Sumit

> diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
> index 49b2e02537dd..5bc4700c4dae 100644
> --- a/drivers/char/hw_random/optee-rng.c
> +++ b/drivers/char/hw_random/optee-rng.c
> @@ -128,7 +128,7 @@ static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
>                 data += rng_size;
>                 read += rng_size;
>
> -               if (wait) {
> +               if (wait && pvt_data->data_rate) {
>                         if (timeout-- == 0)
>                                 return read;
>                         msleep((1000 * (max - read)) / pvt_data->data_rate);
> --
> 2.17.1
>

^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCHv2 2/2] hwrng: optee: fix wait use case
  2020-07-24 13:22   ` Sumit Garg
@ 2020-07-24 14:23     ` Jorge Ramirez-Ortiz, Foundries
  2020-07-28 10:05       ` Jorge Ramirez-Ortiz, Foundries
  2020-08-05 13:49       ` Sumit Garg
  0 siblings, 2 replies; 14+ messages in thread
From: Jorge Ramirez-Ortiz, Foundries @ 2020-07-24 14:23 UTC (permalink / raw)
  To: Sumit Garg
  Cc: Jorge Ramirez-Ortiz, Matt Mackall, Herbert Xu, Jens Wiklander,
	Arnd Bergmann, ricardo, Michael Scott, Greg Kroah-Hartman,
	op-tee, open list:HARDWARE RANDOM NUMBER GENERATOR CORE,
	Linux Kernel Mailing List

On 24/07/20, Sumit Garg wrote:
> On Thu, 23 Jul 2020 at 14:16, Jorge Ramirez-Ortiz <jorge@foundries.io> wrote:
> >
> > The current code waits for data to be available before attempting a
> > second read. However the second read would not be executed as the
> > while loop exits.
> >
> > This fix does not wait if all data has been read and reads a second
> > time if only partial data was retrieved on the first read.
> >
> > This fix also does not attempt to read if not data is requested.
> 
> I am not sure how this is possible, can you elaborate?

currently, if the user sets max 0, get_optee_rng_data will regardless
issuese a call to the secure world requesting 0 bytes from the RNG

with this patch, this request is avoided.

> 
> >
> > Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
> > ---
> >  v2: tidy up the while loop to avoid reading when no data is requested
> >
> >  drivers/char/hw_random/optee-rng.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
> > index 5bc4700c4dae..a99d82949981 100644
> > --- a/drivers/char/hw_random/optee-rng.c
> > +++ b/drivers/char/hw_random/optee-rng.c
> > @@ -122,14 +122,14 @@ static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
> >         if (max > MAX_ENTROPY_REQ_SZ)
> >                 max = MAX_ENTROPY_REQ_SZ;
> >
> > -       while (read == 0) {
> > +       while (read < max) {
> >                 rng_size = get_optee_rng_data(pvt_data, data, (max - read));
> >
> >                 data += rng_size;
> >                 read += rng_size;
> >
> >                 if (wait && pvt_data->data_rate) {
> > -                       if (timeout-- == 0)
> > +                       if ((timeout-- == 0) || (read == max))
> 
> If read == max, would there be any sleep?

no but I see no reason why there should be a wait since we already have
all the data that we need; the msleep is only required when we need to
wait for the RNG to generate entropy for the number of bytes we are
requesting. if we are requesting 0 bytes, the entropy is already
available. at leat this is what makes sense to me.


> 
> -Sumit
> 
> >                                 return read;
> >                         msleep((1000 * (max - read)) / pvt_data->data_rate);
> >                 } else {
> > --
> > 2.17.1
> >

^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCHv2 2/2] hwrng: optee: fix wait use case
  2020-07-24 14:23     ` Jorge Ramirez-Ortiz, Foundries
@ 2020-07-28 10:05       ` Jorge Ramirez-Ortiz, Foundries
  2020-08-05 13:49       ` Sumit Garg
  1 sibling, 0 replies; 14+ messages in thread
From: Jorge Ramirez-Ortiz, Foundries @ 2020-07-28 10:05 UTC (permalink / raw)
  To: Jorge Ramirez-Ortiz, Foundries
  Cc: Sumit Garg, Matt Mackall, Herbert Xu, Jens Wiklander,
	Arnd Bergmann, ricardo, Michael Scott, Greg Kroah-Hartman,
	op-tee, open list:HARDWARE RANDOM NUMBER GENERATOR CORE,
	Linux Kernel Mailing List

On 24/07/20, Jorge Ramirez-Ortiz, Foundries wrote:
> On 24/07/20, Sumit Garg wrote:
> > On Thu, 23 Jul 2020 at 14:16, Jorge Ramirez-Ortiz <jorge@foundries.io> wrote:
> > >
> > > The current code waits for data to be available before attempting a
> > > second read. However the second read would not be executed as the
> > > while loop exits.
> > >
> > > This fix does not wait if all data has been read and reads a second
> > > time if only partial data was retrieved on the first read.
> > >
> > > This fix also does not attempt to read if not data is requested.
> > 
> > I am not sure how this is possible, can you elaborate?
> 
> currently, if the user sets max 0, get_optee_rng_data will regardless
> issuese a call to the secure world requesting 0 bytes from the RNG
> 
> with this patch, this request is avoided.
> 
> > 
> > >
> > > Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
> > > ---
> > >  v2: tidy up the while loop to avoid reading when no data is requested
> > >
> > >  drivers/char/hw_random/optee-rng.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
> > > index 5bc4700c4dae..a99d82949981 100644
> > > --- a/drivers/char/hw_random/optee-rng.c
> > > +++ b/drivers/char/hw_random/optee-rng.c
> > > @@ -122,14 +122,14 @@ static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
> > >         if (max > MAX_ENTROPY_REQ_SZ)
> > >                 max = MAX_ENTROPY_REQ_SZ;
> > >
> > > -       while (read == 0) {
> > > +       while (read < max) {
> > >                 rng_size = get_optee_rng_data(pvt_data, data, (max - read));
> > >
> > >                 data += rng_size;
> > >                 read += rng_size;
> > >
> > >                 if (wait && pvt_data->data_rate) {
> > > -                       if (timeout-- == 0)
> > > +                       if ((timeout-- == 0) || (read == max))
> > 
> > If read == max, would there be any sleep?
> 
> no but I see no reason why there should be a wait since we already have
> all the data that we need; the msleep is only required when we need to
> wait for the RNG to generate entropy for the number of bytes we are
> requesting. if we are requesting 0 bytes, the entropy is already
> available. at leat this is what makes sense to me.
> 
>

any further comments?

> > 
> > -Sumit
> > 
> > >                                 return read;
> > >                         msleep((1000 * (max - read)) / pvt_data->data_rate);
> > >                 } else {
> > > --
> > > 2.17.1
> > >

^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCHv2 2/2] hwrng: optee: fix wait use case
  2020-07-23  8:46 ` [PATCHv2 2/2] hwrng: optee: fix wait use case Jorge Ramirez-Ortiz
  2020-07-24 13:22   ` Sumit Garg
@ 2020-08-05 13:34   ` Jorge Ramirez-Ortiz, Foundries
  1 sibling, 0 replies; 14+ messages in thread
From: Jorge Ramirez-Ortiz, Foundries @ 2020-08-05 13:34 UTC (permalink / raw)
  To: Jorge Ramirez-Ortiz
  Cc: sumit.garg, mpm, herbert, jens.wiklander, arnd, ricardo, mike,
	gregkh, op-tee, linux-crypto, linux-kernel

On 23/07/20, Jorge Ramirez-Ortiz wrote:
> The current code waits for data to be available before attempting a
> second read. However the second read would not be executed as the
> while loop exits.
> 
> This fix does not wait if all data has been read and reads a second
> time if only partial data was retrieved on the first read.
> 
> This fix also does not attempt to read if not data is requested.
> 
> Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
> ---
>  v2: tidy up the while loop to avoid reading when no data is requested
> 
>  drivers/char/hw_random/optee-rng.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
> index 5bc4700c4dae..a99d82949981 100644
> --- a/drivers/char/hw_random/optee-rng.c
> +++ b/drivers/char/hw_random/optee-rng.c
> @@ -122,14 +122,14 @@ static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
>  	if (max > MAX_ENTROPY_REQ_SZ)
>  		max = MAX_ENTROPY_REQ_SZ;
>  
> -	while (read == 0) {
> +	while (read < max) {
>  		rng_size = get_optee_rng_data(pvt_data, data, (max - read));
>  
>  		data += rng_size;
>  		read += rng_size;
>  
>  		if (wait && pvt_data->data_rate) {
> -			if (timeout-- == 0)
> +			if ((timeout-- == 0) || (read == max))
>  				return read;
>  			msleep((1000 * (max - read)) / pvt_data->data_rate);
>  		} else {

any comments please?

^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCHv2 2/2] hwrng: optee: fix wait use case
  2020-07-24 14:23     ` Jorge Ramirez-Ortiz, Foundries
  2020-07-28 10:05       ` Jorge Ramirez-Ortiz, Foundries
@ 2020-08-05 13:49       ` Sumit Garg
  2020-08-05 20:38         ` Jorge Ramirez-Ortiz, Foundries
  1 sibling, 1 reply; 14+ messages in thread
From: Sumit Garg @ 2020-08-05 13:49 UTC (permalink / raw)
  To: Jorge Ramirez-Ortiz, Foundries
  Cc: Matt Mackall, Herbert Xu, Jens Wiklander, Arnd Bergmann, ricardo,
	Michael Scott, Greg Kroah-Hartman, op-tee,
	open list:HARDWARE RANDOM NUMBER GENERATOR CORE,
	Linux Kernel Mailing List

Apologies for my delayed response as I was busy with some other tasks
along with holidays.

On Fri, 24 Jul 2020 at 19:53, Jorge Ramirez-Ortiz, Foundries
<jorge@foundries.io> wrote:
>
> On 24/07/20, Sumit Garg wrote:
> > On Thu, 23 Jul 2020 at 14:16, Jorge Ramirez-Ortiz <jorge@foundries.io> wrote:
> > >
> > > The current code waits for data to be available before attempting a
> > > second read. However the second read would not be executed as the
> > > while loop exits.
> > >
> > > This fix does not wait if all data has been read and reads a second
> > > time if only partial data was retrieved on the first read.
> > >
> > > This fix also does not attempt to read if not data is requested.
> >
> > I am not sure how this is possible, can you elaborate?
>
> currently, if the user sets max 0, get_optee_rng_data will regardless
> issuese a call to the secure world requesting 0 bytes from the RNG
>

This case is already handled by core API: rng_dev_read().

> with this patch, this request is avoided.
>
> >
> > >
> > > Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
> > > ---
> > >  v2: tidy up the while loop to avoid reading when no data is requested
> > >
> > >  drivers/char/hw_random/optee-rng.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
> > > index 5bc4700c4dae..a99d82949981 100644
> > > --- a/drivers/char/hw_random/optee-rng.c
> > > +++ b/drivers/char/hw_random/optee-rng.c
> > > @@ -122,14 +122,14 @@ static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
> > >         if (max > MAX_ENTROPY_REQ_SZ)
> > >                 max = MAX_ENTROPY_REQ_SZ;
> > >
> > > -       while (read == 0) {
> > > +       while (read < max) {
> > >                 rng_size = get_optee_rng_data(pvt_data, data, (max - read));
> > >
> > >                 data += rng_size;
> > >                 read += rng_size;
> > >
> > >                 if (wait && pvt_data->data_rate) {
> > > -                       if (timeout-- == 0)
> > > +                       if ((timeout-- == 0) || (read == max))
> >
> > If read == max, would there be any sleep?
>
> no but I see no reason why there should be a wait since we already have
> all the data that we need; the msleep is only required when we need to
> wait for the RNG to generate entropy for the number of bytes we are
> requesting. if we are requesting 0 bytes, the entropy is already
> available. at leat this is what makes sense to me.
>

Wouldn't it lead to a call as msleep(0); that means no wait as well?

-Sumit

>
> >
> > -Sumit
> >
> > >                                 return read;
> > >                         msleep((1000 * (max - read)) / pvt_data->data_rate);
> > >                 } else {
> > > --
> > > 2.17.1
> > >

^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCHv2 2/2] hwrng: optee: fix wait use case
  2020-08-05 13:49       ` Sumit Garg
@ 2020-08-05 20:38         ` Jorge Ramirez-Ortiz, Foundries
  2020-08-06  6:11           ` Sumit Garg
  0 siblings, 1 reply; 14+ messages in thread
From: Jorge Ramirez-Ortiz, Foundries @ 2020-08-05 20:38 UTC (permalink / raw)
  To: Sumit Garg
  Cc: Jorge Ramirez-Ortiz, Foundries, Matt Mackall, Herbert Xu,
	Jens Wiklander, Arnd Bergmann, ricardo, Michael Scott,
	Greg Kroah-Hartman, op-tee,
	open list:HARDWARE RANDOM NUMBER GENERATOR CORE,
	Linux Kernel Mailing List

On 05/08/20, Sumit Garg wrote:
> Apologies for my delayed response as I was busy with some other tasks
> along with holidays.

no pb! was just making sure this wasnt falling through some cracks.

> 
> On Fri, 24 Jul 2020 at 19:53, Jorge Ramirez-Ortiz, Foundries
> <jorge@foundries.io> wrote:
> >
> > On 24/07/20, Sumit Garg wrote:
> > > On Thu, 23 Jul 2020 at 14:16, Jorge Ramirez-Ortiz <jorge@foundries.io> wrote:
> > > >
> > > > The current code waits for data to be available before attempting a
> > > > second read. However the second read would not be executed as the
> > > > while loop exits.
> > > >
> > > > This fix does not wait if all data has been read and reads a second
> > > > time if only partial data was retrieved on the first read.
> > > >
> > > > This fix also does not attempt to read if not data is requested.
> > >
> > > I am not sure how this is possible, can you elaborate?
> >
> > currently, if the user sets max 0, get_optee_rng_data will regardless
> > issuese a call to the secure world requesting 0 bytes from the RNG
> >
> 
> This case is already handled by core API: rng_dev_read().

ah ok good point, you are right
but yeah, there is no consequence to the actual patch.

> 
> > with this patch, this request is avoided.
> >
> > >
> > > >
> > > > Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
> > > > ---
> > > >  v2: tidy up the while loop to avoid reading when no data is requested
> > > >
> > > >  drivers/char/hw_random/optee-rng.c | 4 ++--
> > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
> > > > index 5bc4700c4dae..a99d82949981 100644
> > > > --- a/drivers/char/hw_random/optee-rng.c
> > > > +++ b/drivers/char/hw_random/optee-rng.c
> > > > @@ -122,14 +122,14 @@ static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
> > > >         if (max > MAX_ENTROPY_REQ_SZ)
> > > >                 max = MAX_ENTROPY_REQ_SZ;
> > > >
> > > > -       while (read == 0) {
> > > > +       while (read < max) {
> > > >                 rng_size = get_optee_rng_data(pvt_data, data, (max - read));
> > > >
> > > >                 data += rng_size;
> > > >                 read += rng_size;
> > > >
> > > >                 if (wait && pvt_data->data_rate) {
> > > > -                       if (timeout-- == 0)
> > > > +                       if ((timeout-- == 0) || (read == max))
> > >
> > > If read == max, would there be any sleep?
> >
> > no but I see no reason why there should be a wait since we already have
> > all the data that we need; the msleep is only required when we need to
> > wait for the RNG to generate entropy for the number of bytes we are
> > requesting. if we are requesting 0 bytes, the entropy is already
> > available. at leat this is what makes sense to me.
> >
> 
> Wouldn't it lead to a call as msleep(0); that means no wait as well?

I dont understand: there is no reason to wait if read == max and this
patch will not wait: if read == max it calls 'return read'

am I misunderstanding your point?

> 
> -Sumit
> 
> >
> > >
> > > -Sumit
> > >
> > > >                                 return read;
> > > >                         msleep((1000 * (max - read)) / pvt_data->data_rate);
> > > >                 } else {
> > > > --
> > > > 2.17.1
> > > >

^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCHv2 2/2] hwrng: optee: fix wait use case
  2020-08-05 20:38         ` Jorge Ramirez-Ortiz, Foundries
@ 2020-08-06  6:11           ` Sumit Garg
  2020-08-06  6:30             ` Jorge Ramirez-Ortiz, Foundries
  0 siblings, 1 reply; 14+ messages in thread
From: Sumit Garg @ 2020-08-06  6:11 UTC (permalink / raw)
  To: Jorge Ramirez-Ortiz, Foundries
  Cc: Matt Mackall, Herbert Xu, Jens Wiklander, Arnd Bergmann, ricardo,
	Michael Scott, Greg Kroah-Hartman, op-tee,
	open list:HARDWARE RANDOM NUMBER GENERATOR CORE,
	Linux Kernel Mailing List

On Thu, 6 Aug 2020 at 02:08, Jorge Ramirez-Ortiz, Foundries
<jorge@foundries.io> wrote:
>
> On 05/08/20, Sumit Garg wrote:
> > Apologies for my delayed response as I was busy with some other tasks
> > along with holidays.
>
> no pb! was just making sure this wasnt falling through some cracks.
>
> >
> > On Fri, 24 Jul 2020 at 19:53, Jorge Ramirez-Ortiz, Foundries
> > <jorge@foundries.io> wrote:
> > >
> > > On 24/07/20, Sumit Garg wrote:
> > > > On Thu, 23 Jul 2020 at 14:16, Jorge Ramirez-Ortiz <jorge@foundries.io> wrote:
> > > > >
> > > > > The current code waits for data to be available before attempting a
> > > > > second read. However the second read would not be executed as the
> > > > > while loop exits.
> > > > >
> > > > > This fix does not wait if all data has been read and reads a second
> > > > > time if only partial data was retrieved on the first read.
> > > > >
> > > > > This fix also does not attempt to read if not data is requested.
> > > >
> > > > I am not sure how this is possible, can you elaborate?
> > >
> > > currently, if the user sets max 0, get_optee_rng_data will regardless
> > > issuese a call to the secure world requesting 0 bytes from the RNG
> > >
> >
> > This case is already handled by core API: rng_dev_read().
>
> ah ok good point, you are right
> but yeah, there is no consequence to the actual patch.
>

So, at least you could get rid of the corresponding text from commit message.

> >
> > > with this patch, this request is avoided.
> > >
> > > >
> > > > >
> > > > > Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
> > > > > ---
> > > > >  v2: tidy up the while loop to avoid reading when no data is requested
> > > > >
> > > > >  drivers/char/hw_random/optee-rng.c | 4 ++--
> > > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
> > > > > index 5bc4700c4dae..a99d82949981 100644
> > > > > --- a/drivers/char/hw_random/optee-rng.c
> > > > > +++ b/drivers/char/hw_random/optee-rng.c
> > > > > @@ -122,14 +122,14 @@ static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
> > > > >         if (max > MAX_ENTROPY_REQ_SZ)
> > > > >                 max = MAX_ENTROPY_REQ_SZ;
> > > > >
> > > > > -       while (read == 0) {
> > > > > +       while (read < max) {
> > > > >                 rng_size = get_optee_rng_data(pvt_data, data, (max - read));
> > > > >
> > > > >                 data += rng_size;
> > > > >                 read += rng_size;
> > > > >
> > > > >                 if (wait && pvt_data->data_rate) {
> > > > > -                       if (timeout-- == 0)
> > > > > +                       if ((timeout-- == 0) || (read == max))
> > > >
> > > > If read == max, would there be any sleep?
> > >
> > > no but I see no reason why there should be a wait since we already have
> > > all the data that we need; the msleep is only required when we need to
> > > wait for the RNG to generate entropy for the number of bytes we are
> > > requesting. if we are requesting 0 bytes, the entropy is already
> > > available. at leat this is what makes sense to me.
> > >
> >
> > Wouldn't it lead to a call as msleep(0); that means no wait as well?
>
> I dont understand: there is no reason to wait if read == max and this
> patch will not wait: if read == max it calls 'return read'
>
> am I misunderstanding your point?

What I mean is that we shouldn't require this extra check here as
there wasn't any wait if read == max with existing implementation too.

-Sumit

>
> >
> > -Sumit
> >
> > >
> > > >
> > > > -Sumit
> > > >
> > > > >                                 return read;
> > > > >                         msleep((1000 * (max - read)) / pvt_data->data_rate);
> > > > >                 } else {
> > > > > --
> > > > > 2.17.1
> > > > >

^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCHv2 2/2] hwrng: optee: fix wait use case
  2020-08-06  6:11           ` Sumit Garg
@ 2020-08-06  6:30             ` Jorge Ramirez-Ortiz, Foundries
  2020-08-06  6:57               ` Sumit Garg
  0 siblings, 1 reply; 14+ messages in thread
From: Jorge Ramirez-Ortiz, Foundries @ 2020-08-06  6:30 UTC (permalink / raw)
  To: Sumit Garg
  Cc: Jorge Ramirez-Ortiz, Foundries, Matt Mackall, Herbert Xu,
	Jens Wiklander, Arnd Bergmann, ricardo, Michael Scott,
	Greg Kroah-Hartman, op-tee,
	open list:HARDWARE RANDOM NUMBER GENERATOR CORE,
	Linux Kernel Mailing List

On 06/08/20, Sumit Garg wrote:
> On Thu, 6 Aug 2020 at 02:08, Jorge Ramirez-Ortiz, Foundries
> <jorge@foundries.io> wrote:
> >
> > On 05/08/20, Sumit Garg wrote:
> > > Apologies for my delayed response as I was busy with some other tasks
> > > along with holidays.
> >
> > no pb! was just making sure this wasnt falling through some cracks.
> >
> > >
> > > On Fri, 24 Jul 2020 at 19:53, Jorge Ramirez-Ortiz, Foundries
> > > <jorge@foundries.io> wrote:
> > > >
> > > > On 24/07/20, Sumit Garg wrote:
> > > > > On Thu, 23 Jul 2020 at 14:16, Jorge Ramirez-Ortiz <jorge@foundries.io> wrote:
> > > > > >
> > > > > > The current code waits for data to be available before attempting a
> > > > > > second read. However the second read would not be executed as the
> > > > > > while loop exits.
> > > > > >
> > > > > > This fix does not wait if all data has been read and reads a second
> > > > > > time if only partial data was retrieved on the first read.
> > > > > >
> > > > > > This fix also does not attempt to read if not data is requested.
> > > > >
> > > > > I am not sure how this is possible, can you elaborate?
> > > >
> > > > currently, if the user sets max 0, get_optee_rng_data will regardless
> > > > issuese a call to the secure world requesting 0 bytes from the RNG
> > > >
> > >
> > > This case is already handled by core API: rng_dev_read().
> >
> > ah ok good point, you are right
> > but yeah, there is no consequence to the actual patch.
> >
> 
> So, at least you could get rid of the corresponding text from commit message.
> 
> > >
> > > > with this patch, this request is avoided.
> > > >
> > > > >
> > > > > >
> > > > > > Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
> > > > > > ---
> > > > > >  v2: tidy up the while loop to avoid reading when no data is requested
> > > > > >
> > > > > >  drivers/char/hw_random/optee-rng.c | 4 ++--
> > > > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
> > > > > > index 5bc4700c4dae..a99d82949981 100644
> > > > > > --- a/drivers/char/hw_random/optee-rng.c
> > > > > > +++ b/drivers/char/hw_random/optee-rng.c
> > > > > > @@ -122,14 +122,14 @@ static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
> > > > > >         if (max > MAX_ENTROPY_REQ_SZ)
> > > > > >                 max = MAX_ENTROPY_REQ_SZ;
> > > > > >
> > > > > > -       while (read == 0) {
> > > > > > +       while (read < max) {
> > > > > >                 rng_size = get_optee_rng_data(pvt_data, data, (max - read));
> > > > > >
> > > > > >                 data += rng_size;
> > > > > >                 read += rng_size;
> > > > > >
> > > > > >                 if (wait && pvt_data->data_rate) {
> > > > > > -                       if (timeout-- == 0)
> > > > > > +                       if ((timeout-- == 0) || (read == max))
> > > > >
> > > > > If read == max, would there be any sleep?
> > > >
> > > > no but I see no reason why there should be a wait since we already have
> > > > all the data that we need; the msleep is only required when we need to
> > > > wait for the RNG to generate entropy for the number of bytes we are
> > > > requesting. if we are requesting 0 bytes, the entropy is already
> > > > available. at leat this is what makes sense to me.
> > > >
> > >
> > > Wouldn't it lead to a call as msleep(0); that means no wait as well?
> >
> > I dont understand: there is no reason to wait if read == max and this
> > patch will not wait: if read == max it calls 'return read'
> >
> > am I misunderstanding your point?
> 
> What I mean is that we shouldn't require this extra check here as
> there wasn't any wait if read == max with existing implementation too.

um, I am getting confused Sumit

with the exisiting implementation (the one we aim to replace), if get_optee_rng_data reads all the values requested on the first call (ie, read = 0) with wait set to true, the call will wait with msleep(0). Which is unnecessary and waits for a jiffy (ie, the call to msleep 0 will schedule a one jiffy timeout interrruptible)

with this alternative implementation, msleep(0) does not get called.

are we in synch?

> 
> -Sumit
> 
> >
> > >
> > > -Sumit
> > >
> > > >
> > > > >
> > > > > -Sumit
> > > > >
> > > > > >                                 return read;
> > > > > >                         msleep((1000 * (max - read)) / pvt_data->data_rate);
> > > > > >                 } else {
> > > > > > --
> > > > > > 2.17.1
> > > > > >

^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCHv2 2/2] hwrng: optee: fix wait use case
  2020-08-06  6:30             ` Jorge Ramirez-Ortiz, Foundries
@ 2020-08-06  6:57               ` Sumit Garg
  2020-08-06  8:14                 ` Jorge Ramirez-Ortiz, Foundries
  0 siblings, 1 reply; 14+ messages in thread
From: Sumit Garg @ 2020-08-06  6:57 UTC (permalink / raw)
  To: Jorge Ramirez-Ortiz, Foundries
  Cc: Matt Mackall, Herbert Xu, Jens Wiklander, Arnd Bergmann, ricardo,
	Michael Scott, Greg Kroah-Hartman, op-tee,
	open list:HARDWARE RANDOM NUMBER GENERATOR CORE,
	Linux Kernel Mailing List

On Thu, 6 Aug 2020 at 12:00, Jorge Ramirez-Ortiz, Foundries
<jorge@foundries.io> wrote:
>
> On 06/08/20, Sumit Garg wrote:
> > On Thu, 6 Aug 2020 at 02:08, Jorge Ramirez-Ortiz, Foundries
> > <jorge@foundries.io> wrote:
> > >
> > > On 05/08/20, Sumit Garg wrote:
> > > > Apologies for my delayed response as I was busy with some other tasks
> > > > along with holidays.
> > >
> > > no pb! was just making sure this wasnt falling through some cracks.
> > >
> > > >
> > > > On Fri, 24 Jul 2020 at 19:53, Jorge Ramirez-Ortiz, Foundries
> > > > <jorge@foundries.io> wrote:
> > > > >
> > > > > On 24/07/20, Sumit Garg wrote:
> > > > > > On Thu, 23 Jul 2020 at 14:16, Jorge Ramirez-Ortiz <jorge@foundries.io> wrote:
> > > > > > >
> > > > > > > The current code waits for data to be available before attempting a
> > > > > > > second read. However the second read would not be executed as the
> > > > > > > while loop exits.
> > > > > > >
> > > > > > > This fix does not wait if all data has been read and reads a second
> > > > > > > time if only partial data was retrieved on the first read.
> > > > > > >
> > > > > > > This fix also does not attempt to read if not data is requested.
> > > > > >
> > > > > > I am not sure how this is possible, can you elaborate?
> > > > >
> > > > > currently, if the user sets max 0, get_optee_rng_data will regardless
> > > > > issuese a call to the secure world requesting 0 bytes from the RNG
> > > > >
> > > >
> > > > This case is already handled by core API: rng_dev_read().
> > >
> > > ah ok good point, you are right
> > > but yeah, there is no consequence to the actual patch.
> > >
> >
> > So, at least you could get rid of the corresponding text from commit message.
> >
> > > >
> > > > > with this patch, this request is avoided.
> > > > >
> > > > > >
> > > > > > >
> > > > > > > Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
> > > > > > > ---
> > > > > > >  v2: tidy up the while loop to avoid reading when no data is requested
> > > > > > >
> > > > > > >  drivers/char/hw_random/optee-rng.c | 4 ++--
> > > > > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > > > >
> > > > > > > diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
> > > > > > > index 5bc4700c4dae..a99d82949981 100644
> > > > > > > --- a/drivers/char/hw_random/optee-rng.c
> > > > > > > +++ b/drivers/char/hw_random/optee-rng.c
> > > > > > > @@ -122,14 +122,14 @@ static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
> > > > > > >         if (max > MAX_ENTROPY_REQ_SZ)
> > > > > > >                 max = MAX_ENTROPY_REQ_SZ;
> > > > > > >
> > > > > > > -       while (read == 0) {
> > > > > > > +       while (read < max) {
> > > > > > >                 rng_size = get_optee_rng_data(pvt_data, data, (max - read));
> > > > > > >
> > > > > > >                 data += rng_size;
> > > > > > >                 read += rng_size;
> > > > > > >
> > > > > > >                 if (wait && pvt_data->data_rate) {
> > > > > > > -                       if (timeout-- == 0)
> > > > > > > +                       if ((timeout-- == 0) || (read == max))
> > > > > >
> > > > > > If read == max, would there be any sleep?
> > > > >
> > > > > no but I see no reason why there should be a wait since we already have
> > > > > all the data that we need; the msleep is only required when we need to
> > > > > wait for the RNG to generate entropy for the number of bytes we are
> > > > > requesting. if we are requesting 0 bytes, the entropy is already
> > > > > available. at leat this is what makes sense to me.
> > > > >
> > > >
> > > > Wouldn't it lead to a call as msleep(0); that means no wait as well?
> > >
> > > I dont understand: there is no reason to wait if read == max and this
> > > patch will not wait: if read == max it calls 'return read'
> > >
> > > am I misunderstanding your point?
> >
> > What I mean is that we shouldn't require this extra check here as
> > there wasn't any wait if read == max with existing implementation too.
>
> um, I am getting confused Sumit
>
> with the exisiting implementation (the one we aim to replace), if get_optee_rng_data reads all the values requested on the first call (ie, read = 0) with wait set to true, the call will wait with msleep(0). Which is unnecessary and waits for a jiffy (ie, the call to msleep 0 will schedule a one jiffy timeout interrruptible)
>
> with this alternative implementation, msleep(0) does not get called.
>
> are we in synch?

Ah, I see msleep(0) also by default schedules timeout for 1 jiffy. So
we are in sync now. Probably you can clarify this in commit message as
well to avoid confusion.

-Sumit

>
> >
> > -Sumit
> >
> > >
> > > >
> > > > -Sumit
> > > >
> > > > >
> > > > > >
> > > > > > -Sumit
> > > > > >
> > > > > > >                                 return read;
> > > > > > >                         msleep((1000 * (max - read)) / pvt_data->data_rate);
> > > > > > >                 } else {
> > > > > > > --
> > > > > > > 2.17.1
> > > > > > >

^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCHv2 2/2] hwrng: optee: fix wait use case
  2020-08-06  6:57               ` Sumit Garg
@ 2020-08-06  8:14                 ` Jorge Ramirez-Ortiz, Foundries
  2020-08-06  9:15                   ` Sumit Garg
  0 siblings, 1 reply; 14+ messages in thread
From: Jorge Ramirez-Ortiz, Foundries @ 2020-08-06  8:14 UTC (permalink / raw)
  To: Sumit Garg
  Cc: Jorge Ramirez-Ortiz, Foundries, Matt Mackall, Herbert Xu,
	Jens Wiklander, Arnd Bergmann, ricardo, Michael Scott,
	Greg Kroah-Hartman, op-tee,
	open list:HARDWARE RANDOM NUMBER GENERATOR CORE,
	Linux Kernel Mailing List

On 06/08/20, Sumit Garg wrote:
> On Thu, 6 Aug 2020 at 12:00, Jorge Ramirez-Ortiz, Foundries
> <jorge@foundries.io> wrote:
> >
> > On 06/08/20, Sumit Garg wrote:
> > > On Thu, 6 Aug 2020 at 02:08, Jorge Ramirez-Ortiz, Foundries
> > > <jorge@foundries.io> wrote:
> > > >
> > > > On 05/08/20, Sumit Garg wrote:
> > > > > Apologies for my delayed response as I was busy with some other tasks
> > > > > along with holidays.
> > > >
> > > > no pb! was just making sure this wasnt falling through some cracks.
> > > >
> > > > >
> > > > > On Fri, 24 Jul 2020 at 19:53, Jorge Ramirez-Ortiz, Foundries
> > > > > <jorge@foundries.io> wrote:
> > > > > >
> > > > > > On 24/07/20, Sumit Garg wrote:
> > > > > > > On Thu, 23 Jul 2020 at 14:16, Jorge Ramirez-Ortiz <jorge@foundries.io> wrote:
> > > > > > > >
> > > > > > > > The current code waits for data to be available before attempting a
> > > > > > > > second read. However the second read would not be executed as the
> > > > > > > > while loop exits.
> > > > > > > >
> > > > > > > > This fix does not wait if all data has been read and reads a second
> > > > > > > > time if only partial data was retrieved on the first read.
> > > > > > > >
> > > > > > > > This fix also does not attempt to read if not data is requested.
> > > > > > >
> > > > > > > I am not sure how this is possible, can you elaborate?
> > > > > >
> > > > > > currently, if the user sets max 0, get_optee_rng_data will regardless
> > > > > > issuese a call to the secure world requesting 0 bytes from the RNG
> > > > > >
> > > > >
> > > > > This case is already handled by core API: rng_dev_read().
> > > >
> > > > ah ok good point, you are right
> > > > but yeah, there is no consequence to the actual patch.
> > > >
> > >
> > > So, at least you could get rid of the corresponding text from commit message.
> > >
> > > > >
> > > > > > with this patch, this request is avoided.
> > > > > >
> > > > > > >
> > > > > > > >
> > > > > > > > Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
> > > > > > > > ---
> > > > > > > >  v2: tidy up the while loop to avoid reading when no data is requested
> > > > > > > >
> > > > > > > >  drivers/char/hw_random/optee-rng.c | 4 ++--
> > > > > > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > > > > >
> > > > > > > > diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
> > > > > > > > index 5bc4700c4dae..a99d82949981 100644
> > > > > > > > --- a/drivers/char/hw_random/optee-rng.c
> > > > > > > > +++ b/drivers/char/hw_random/optee-rng.c
> > > > > > > > @@ -122,14 +122,14 @@ static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
> > > > > > > >         if (max > MAX_ENTROPY_REQ_SZ)
> > > > > > > >                 max = MAX_ENTROPY_REQ_SZ;
> > > > > > > >
> > > > > > > > -       while (read == 0) {
> > > > > > > > +       while (read < max) {
> > > > > > > >                 rng_size = get_optee_rng_data(pvt_data, data, (max - read));
> > > > > > > >
> > > > > > > >                 data += rng_size;
> > > > > > > >                 read += rng_size;
> > > > > > > >
> > > > > > > >                 if (wait && pvt_data->data_rate) {
> > > > > > > > -                       if (timeout-- == 0)
> > > > > > > > +                       if ((timeout-- == 0) || (read == max))
> > > > > > >
> > > > > > > If read == max, would there be any sleep?
> > > > > >
> > > > > > no but I see no reason why there should be a wait since we already have
> > > > > > all the data that we need; the msleep is only required when we need to
> > > > > > wait for the RNG to generate entropy for the number of bytes we are
> > > > > > requesting. if we are requesting 0 bytes, the entropy is already
> > > > > > available. at leat this is what makes sense to me.
> > > > > >
> > > > >
> > > > > Wouldn't it lead to a call as msleep(0); that means no wait as well?
> > > >
> > > > I dont understand: there is no reason to wait if read == max and this
> > > > patch will not wait: if read == max it calls 'return read'
> > > >
> > > > am I misunderstanding your point?
> > >
> > > What I mean is that we shouldn't require this extra check here as
> > > there wasn't any wait if read == max with existing implementation too.
> >
> > um, I am getting confused Sumit
> >
> > with the exisiting implementation (the one we aim to replace), if get_optee_rng_data reads all the values requested on the first call (ie, read = 0) with wait set to true, the call will wait with msleep(0). Which is unnecessary and waits for a jiffy (ie, the call to msleep 0 will schedule a one jiffy timeout interrruptible)
> >
> > with this alternative implementation, msleep(0) does not get called.
> >
> > are we in synch?
> 
> Ah, I see msleep(0) also by default schedules timeout for 1 jiffy. So
> we are in sync now. Probably you can clarify this in commit message as
> well to avoid confusion.

ok will do.
shall I add your reviewed-by line or just resend?

> 
> -Sumit
> 
> >
> > >
> > > -Sumit
> > >
> > > >
> > > > >
> > > > > -Sumit
> > > > >
> > > > > >
> > > > > > >
> > > > > > > -Sumit
> > > > > > >
> > > > > > > >                                 return read;
> > > > > > > >                         msleep((1000 * (max - read)) / pvt_data->data_rate);
> > > > > > > >                 } else {
> > > > > > > > --
> > > > > > > > 2.17.1
> > > > > > > >

^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCHv2 2/2] hwrng: optee: fix wait use case
  2020-08-06  8:14                 ` Jorge Ramirez-Ortiz, Foundries
@ 2020-08-06  9:15                   ` Sumit Garg
  0 siblings, 0 replies; 14+ messages in thread
From: Sumit Garg @ 2020-08-06  9:15 UTC (permalink / raw)
  To: Jorge Ramirez-Ortiz, Foundries
  Cc: Matt Mackall, Herbert Xu, Jens Wiklander, Arnd Bergmann, ricardo,
	Michael Scott, Greg Kroah-Hartman, op-tee,
	open list:HARDWARE RANDOM NUMBER GENERATOR CORE,
	Linux Kernel Mailing List

On Thu, 6 Aug 2020 at 13:44, Jorge Ramirez-Ortiz, Foundries
<jorge@foundries.io> wrote:
>
> On 06/08/20, Sumit Garg wrote:
> > On Thu, 6 Aug 2020 at 12:00, Jorge Ramirez-Ortiz, Foundries
> > <jorge@foundries.io> wrote:
> > >
> > > On 06/08/20, Sumit Garg wrote:
> > > > On Thu, 6 Aug 2020 at 02:08, Jorge Ramirez-Ortiz, Foundries
> > > > <jorge@foundries.io> wrote:
> > > > >
> > > > > On 05/08/20, Sumit Garg wrote:
> > > > > > Apologies for my delayed response as I was busy with some other tasks
> > > > > > along with holidays.
> > > > >
> > > > > no pb! was just making sure this wasnt falling through some cracks.
> > > > >
> > > > > >
> > > > > > On Fri, 24 Jul 2020 at 19:53, Jorge Ramirez-Ortiz, Foundries
> > > > > > <jorge@foundries.io> wrote:
> > > > > > >
> > > > > > > On 24/07/20, Sumit Garg wrote:
> > > > > > > > On Thu, 23 Jul 2020 at 14:16, Jorge Ramirez-Ortiz <jorge@foundries.io> wrote:
> > > > > > > > >
> > > > > > > > > The current code waits for data to be available before attempting a
> > > > > > > > > second read. However the second read would not be executed as the
> > > > > > > > > while loop exits.
> > > > > > > > >
> > > > > > > > > This fix does not wait if all data has been read and reads a second
> > > > > > > > > time if only partial data was retrieved on the first read.
> > > > > > > > >
> > > > > > > > > This fix also does not attempt to read if not data is requested.
> > > > > > > >
> > > > > > > > I am not sure how this is possible, can you elaborate?
> > > > > > >
> > > > > > > currently, if the user sets max 0, get_optee_rng_data will regardless
> > > > > > > issuese a call to the secure world requesting 0 bytes from the RNG
> > > > > > >
> > > > > >
> > > > > > This case is already handled by core API: rng_dev_read().
> > > > >
> > > > > ah ok good point, you are right
> > > > > but yeah, there is no consequence to the actual patch.
> > > > >
> > > >
> > > > So, at least you could get rid of the corresponding text from commit message.
> > > >
> > > > > >
> > > > > > > with this patch, this request is avoided.
> > > > > > >
> > > > > > > >
> > > > > > > > >
> > > > > > > > > Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
> > > > > > > > > ---
> > > > > > > > >  v2: tidy up the while loop to avoid reading when no data is requested
> > > > > > > > >
> > > > > > > > >  drivers/char/hw_random/optee-rng.c | 4 ++--
> > > > > > > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > > > > > >
> > > > > > > > > diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
> > > > > > > > > index 5bc4700c4dae..a99d82949981 100644
> > > > > > > > > --- a/drivers/char/hw_random/optee-rng.c
> > > > > > > > > +++ b/drivers/char/hw_random/optee-rng.c
> > > > > > > > > @@ -122,14 +122,14 @@ static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
> > > > > > > > >         if (max > MAX_ENTROPY_REQ_SZ)
> > > > > > > > >                 max = MAX_ENTROPY_REQ_SZ;
> > > > > > > > >
> > > > > > > > > -       while (read == 0) {
> > > > > > > > > +       while (read < max) {
> > > > > > > > >                 rng_size = get_optee_rng_data(pvt_data, data, (max - read));
> > > > > > > > >
> > > > > > > > >                 data += rng_size;
> > > > > > > > >                 read += rng_size;
> > > > > > > > >
> > > > > > > > >                 if (wait && pvt_data->data_rate) {
> > > > > > > > > -                       if (timeout-- == 0)
> > > > > > > > > +                       if ((timeout-- == 0) || (read == max))
> > > > > > > >
> > > > > > > > If read == max, would there be any sleep?
> > > > > > >
> > > > > > > no but I see no reason why there should be a wait since we already have
> > > > > > > all the data that we need; the msleep is only required when we need to
> > > > > > > wait for the RNG to generate entropy for the number of bytes we are
> > > > > > > requesting. if we are requesting 0 bytes, the entropy is already
> > > > > > > available. at leat this is what makes sense to me.
> > > > > > >
> > > > > >
> > > > > > Wouldn't it lead to a call as msleep(0); that means no wait as well?
> > > > >
> > > > > I dont understand: there is no reason to wait if read == max and this
> > > > > patch will not wait: if read == max it calls 'return read'
> > > > >
> > > > > am I misunderstanding your point?
> > > >
> > > > What I mean is that we shouldn't require this extra check here as
> > > > there wasn't any wait if read == max with existing implementation too.
> > >
> > > um, I am getting confused Sumit
> > >
> > > with the exisiting implementation (the one we aim to replace), if get_optee_rng_data reads all the values requested on the first call (ie, read = 0) with wait set to true, the call will wait with msleep(0). Which is unnecessary and waits for a jiffy (ie, the call to msleep 0 will schedule a one jiffy timeout interrruptible)
> > >
> > > with this alternative implementation, msleep(0) does not get called.
> > >
> > > are we in synch?
> >
> > Ah, I see msleep(0) also by default schedules timeout for 1 jiffy. So
> > we are in sync now. Probably you can clarify this in commit message as
> > well to avoid confusion.
>
> ok will do.
> shall I add your reviewed-by line or just resend?
>

Yes it's fine with me to add mine reviewed-by.

> >
> > -Sumit
> >
> > >
> > > >
> > > > -Sumit
> > > >
> > > > >
> > > > > >
> > > > > > -Sumit
> > > > > >
> > > > > > >
> > > > > > > >
> > > > > > > > -Sumit
> > > > > > > >
> > > > > > > > >                                 return read;
> > > > > > > > >                         msleep((1000 * (max - read)) / pvt_data->data_rate);
> > > > > > > > >                 } else {
> > > > > > > > > --
> > > > > > > > > 2.17.1
> > > > > > > > >

^ permalink raw reply	[flat|nested] 14+ messages in thread

end of thread, back to index

Thread overview: 14+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-07-23  8:46 [PATCHv2 1/2] hwrng: optee: handle unlimited data rates Jorge Ramirez-Ortiz
2020-07-23  8:46 ` [PATCHv2 2/2] hwrng: optee: fix wait use case Jorge Ramirez-Ortiz
2020-07-24 13:22   ` Sumit Garg
2020-07-24 14:23     ` Jorge Ramirez-Ortiz, Foundries
2020-07-28 10:05       ` Jorge Ramirez-Ortiz, Foundries
2020-08-05 13:49       ` Sumit Garg
2020-08-05 20:38         ` Jorge Ramirez-Ortiz, Foundries
2020-08-06  6:11           ` Sumit Garg
2020-08-06  6:30             ` Jorge Ramirez-Ortiz, Foundries
2020-08-06  6:57               ` Sumit Garg
2020-08-06  8:14                 ` Jorge Ramirez-Ortiz, Foundries
2020-08-06  9:15                   ` Sumit Garg
2020-08-05 13:34   ` Jorge Ramirez-Ortiz, Foundries
2020-07-24 13:24 ` [PATCHv2 1/2] hwrng: optee: handle unlimited data rates Sumit Garg

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