diff mbox series

[1/3] xen: check required Xen features

Message ID 20210422151007.2205-2-jgross@suse.com (mailing list archive)
State New
Headers show
Series xen: remove some checks for always present Xen features | expand

Commit Message

Juergen Gross April 22, 2021, 3:10 p.m. UTC
Linux kernel is not supported to run on Xen versions older than 4.0.

Add tests for required Xen features always being present in Xen 4.0
and newer.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 drivers/xen/features.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

Comments

Stefano Stabellini April 22, 2021, 3:26 p.m. UTC | #1
On Thu, 22 Apr 2021, Juergen Gross wrote:
> Linux kernel is not supported to run on Xen versions older than 4.0.
> 
> Add tests for required Xen features always being present in Xen 4.0
> and newer.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
>  drivers/xen/features.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/xen/features.c b/drivers/xen/features.c
> index 25c053b09605..60503299c9bc 100644
> --- a/drivers/xen/features.c
> +++ b/drivers/xen/features.c
> @@ -9,13 +9,26 @@
>  #include <linux/types.h>
>  #include <linux/cache.h>
>  #include <linux/export.h>
> +#include <linux/printk.h>
>  
>  #include <asm/xen/hypercall.h>
>  
> +#include <xen/xen.h>
>  #include <xen/interface/xen.h>
>  #include <xen/interface/version.h>
>  #include <xen/features.h>
>  
> +/*
> + * Linux kernel expects at least Xen 4.0.
> + *
> + * Assume some features to be available for that reason (depending on guest
> + * mode, of course).
> + */
> +#define chk_feature(f) {						\
> +		if (!xen_feature(f))					\
> +			pr_err("Xen: feature %s not available!\n", #f);	\
> +	}

I think this could be done as a static inline function in
include/xen/features.h. That way it would be available everywhere. Also,
static inlines are better than macro when it is possible to use them in
terms of code safety.


>  u8 xen_features[XENFEAT_NR_SUBMAPS * 32] __read_mostly;
>  EXPORT_SYMBOL_GPL(xen_features);
>  
> @@ -31,4 +44,9 @@ void xen_setup_features(void)
>  		for (j = 0; j < 32; j++)
>  			xen_features[i * 32 + j] = !!(fi.submap & 1<<j);
>  	}
> +
> +	if (xen_pv_domain()) {
> +		chk_feature(XENFEAT_mmu_pt_update_preserve_ad);
> +		chk_feature(XENFEAT_gnttab_map_avail_bits);
> +	}
>  }
> -- 
> 2.26.2
>
Juergen Gross April 22, 2021, 3:32 p.m. UTC | #2
On 22.04.21 17:26, Stefano Stabellini wrote:
> On Thu, 22 Apr 2021, Juergen Gross wrote:
>> Linux kernel is not supported to run on Xen versions older than 4.0.
>>
>> Add tests for required Xen features always being present in Xen 4.0
>> and newer.
>>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>> ---
>>   drivers/xen/features.c | 18 ++++++++++++++++++
>>   1 file changed, 18 insertions(+)
>>
>> diff --git a/drivers/xen/features.c b/drivers/xen/features.c
>> index 25c053b09605..60503299c9bc 100644
>> --- a/drivers/xen/features.c
>> +++ b/drivers/xen/features.c
>> @@ -9,13 +9,26 @@
>>   #include <linux/types.h>
>>   #include <linux/cache.h>
>>   #include <linux/export.h>
>> +#include <linux/printk.h>
>>   
>>   #include <asm/xen/hypercall.h>
>>   
>> +#include <xen/xen.h>
>>   #include <xen/interface/xen.h>
>>   #include <xen/interface/version.h>
>>   #include <xen/features.h>
>>   
>> +/*
>> + * Linux kernel expects at least Xen 4.0.
>> + *
>> + * Assume some features to be available for that reason (depending on guest
>> + * mode, of course).
>> + */
>> +#define chk_feature(f) {						\
>> +		if (!xen_feature(f))					\
>> +			pr_err("Xen: feature %s not available!\n", #f);	\
>> +	}
> 
> I think this could be done as a static inline function in
> include/xen/features.h. That way it would be available everywhere. Also,
> static inlines are better than macro when it is possible to use them in
> terms of code safety.

It is a macro in order to have only one parameter.

And being a local macro is rendering the code safety reasoning moot.

Additionally I don't want this testing to be scattered all over the
code base. It should be done in one place only.


Juergen
Boris Ostrovsky May 10, 2021, 12:11 p.m. UTC | #3
On 4/22/21 11:10 AM, Juergen Gross wrote:
>  
> +/*
> + * Linux kernel expects at least Xen 4.0.
> + *
> + * Assume some features to be available for that reason (depending on guest
> + * mode, of course).
> + */
> +#define chk_feature(f) {						\
> +		if (!xen_feature(f))					\
> +			pr_err("Xen: feature %s not available!\n", #f);	\
> +	}


With your changes in the subsequent patches, are we still going to function properly without those features? (i.e. maybe we should just panic)


(Also, chk_required_features() perhaps?)


-boris


> +
>  u8 xen_features[XENFEAT_NR_SUBMAPS * 32] __read_mostly;
>  EXPORT_SYMBOL_GPL(xen_features);
>  
> @@ -31,4 +44,9 @@ void xen_setup_features(void)
>  		for (j = 0; j < 32; j++)
>  			xen_features[i * 32 + j] = !!(fi.submap & 1<<j);
>  	}
> +
> +	if (xen_pv_domain()) {
> +		chk_feature(XENFEAT_mmu_pt_update_preserve_ad);
> +		chk_feature(XENFEAT_gnttab_map_avail_bits);
> +	}
>  }
Juergen Gross May 10, 2021, 1:21 p.m. UTC | #4
On 10.05.21 14:11, Boris Ostrovsky wrote:
> 
> On 4/22/21 11:10 AM, Juergen Gross wrote:
>>   
>> +/*
>> + * Linux kernel expects at least Xen 4.0.
>> + *
>> + * Assume some features to be available for that reason (depending on guest
>> + * mode, of course).
>> + */
>> +#define chk_feature(f) {						\
>> +		if (!xen_feature(f))					\
>> +			pr_err("Xen: feature %s not available!\n", #f);	\
>> +	}
> 
> 
> With your changes in the subsequent patches, are we still going to function properly without those features? (i.e. maybe we should just panic)

Depends on the use case.

XENFEAT_gnttab_map_avail_bits is relevant for driver domains using
user space backends only. In case it is not available "interesting"
things might happen.

XENFEAT_mmu_pt_update_preserve_ad not being present would result in
a subsequent mmu-update function using that feature returning -ENOSYS,
so this wouldn't be unrecognized.

So panic() might be a good idea in case the features are not available.

> (Also, chk_required_features() perhaps?)

Fine with me.


Juergen
diff mbox series

Patch

diff --git a/drivers/xen/features.c b/drivers/xen/features.c
index 25c053b09605..60503299c9bc 100644
--- a/drivers/xen/features.c
+++ b/drivers/xen/features.c
@@ -9,13 +9,26 @@ 
 #include <linux/types.h>
 #include <linux/cache.h>
 #include <linux/export.h>
+#include <linux/printk.h>
 
 #include <asm/xen/hypercall.h>
 
+#include <xen/xen.h>
 #include <xen/interface/xen.h>
 #include <xen/interface/version.h>
 #include <xen/features.h>
 
+/*
+ * Linux kernel expects at least Xen 4.0.
+ *
+ * Assume some features to be available for that reason (depending on guest
+ * mode, of course).
+ */
+#define chk_feature(f) {						\
+		if (!xen_feature(f))					\
+			pr_err("Xen: feature %s not available!\n", #f);	\
+	}
+
 u8 xen_features[XENFEAT_NR_SUBMAPS * 32] __read_mostly;
 EXPORT_SYMBOL_GPL(xen_features);
 
@@ -31,4 +44,9 @@  void xen_setup_features(void)
 		for (j = 0; j < 32; j++)
 			xen_features[i * 32 + j] = !!(fi.submap & 1<<j);
 	}
+
+	if (xen_pv_domain()) {
+		chk_feature(XENFEAT_mmu_pt_update_preserve_ad);
+		chk_feature(XENFEAT_gnttab_map_avail_bits);
+	}
 }