Re: [Xen-devel] [PATCH v6 09/12] xen: add runtime parameter access support to hypfs

["Jürgen Groß" <jgross@suse.com>]

On 04.03.20 12:32, Jan Beulich wrote:
> On 26.02.2020 13:47, Juergen Gross wrote:
>> --- a/xen/arch/x86/hvm/vmx/vmcs.c
>> +++ b/xen/arch/x86/hvm/vmx/vmcs.c
>> @@ -70,6 +70,30 @@ integer_param("ple_window", ple_window);
>>   static bool __read_mostly opt_ept_pml = true;
>>   static s8 __read_mostly opt_ept_ad = -1;
>>   int8_t __read_mostly opt_ept_exec_sp = -1;
>> +static char opt_ept_setting[16];
> 
> I don't think this is quite big enough.

Yes, you are right.

> 
>> +static void update_ept_param_append(const char *str, int val)
>> +{
>> +    char *pos = opt_ept_setting + strlen(opt_ept_setting);
>> +
>> +    snprintf(pos, sizeof(opt_ept_setting) - (pos - opt_ept_setting),
>> +             ",%s=%d", str, val);
>> +}
>> +
>> +static void update_ept_param(void)
>> +{
>> +    snprintf(opt_ept_setting, sizeof(opt_ept_setting), "pml=%d", opt_ept_pml);
>> +    if ( opt_ept_ad >= 0 )
>> +        update_ept_param_append("ad", opt_ept_ad);
> 
> This won't correctly reflect reality: If you look at
> vmx_init_vmcs_config(), even a negative value means "true" here,
> unless on a specific Atom model. I think init_ept_param() wants
> to have that erratum workaround logic moved there, such that
> you can then assme the value to be non-negative here.

But isn't not mentioning it in the -1 case correct? -1 means: do the
correct thing on the current hardware.

In case we want to report an explicit value for "ad" we should add a
node for that purpose.

>> +    if ( opt_ept_exec_sp >= 0 )
>> +        update_ept_param_append("exec-sp", opt_ept_exec_sp);
> 
> I agree for this one - if the value is still -1, it has neither
> been set nor is its value of any interest.
> 
>> +static void __init init_ept_param(struct param_hypfs *par)
>> +{
>> +    custom_runtime_set_var(par, opt_ept_setting);
>> +    update_ept_param();
>> +}
>>   
>>   static int __init parse_ept_param(const char *s)
>>   {
>> @@ -93,6 +117,8 @@ static int __init parse_ept_param(const char *s)
>>           s = ss + 1;
>>       } while ( *ss );
>>   
>> +    update_ept_param();
> 
> Isn't this redundant with the use in init_ept_param() (or the
> other way around - there should be clear ordering between the
> command line parsing functions and the param-init ones, I would
> suppose)?

You are right. I can drop this call, as the param-init call will
come later.

> 
>> --- a/xen/arch/x86/pv/domain.c
>> +++ b/xen/arch/x86/pv/domain.c
>> @@ -20,8 +20,27 @@ static __read_mostly enum {
>>       PCID_OFF,
>>       PCID_ALL,
>>       PCID_XPTI,
>> -    PCID_NOXPTI
>> +    PCID_NOXPTI,
>> +    PCID_END
>>   } opt_pcid = PCID_XPTI;
>> +static const char *opt_pcid_2_string[PCID_END] = {
> 
> You either want another const here, or (more space efficient) you
> want to use const char[PCID_END][7].

Ah, right, good idea.

> 
>> +    [PCID_OFF] = "off",
>> +    [PCID_ALL] = "on",
>> +    [PCID_XPTI] = "xpti",
>> +    [PCID_NOXPTI] = "noxpti"
>> +};
>> +static char opt_pcid_val[7];
>> +
>> +static void update_opt_pcid(void)
>> +{
>> +    strlcpy(opt_pcid_val, opt_pcid_2_string[opt_pcid], sizeof(opt_pcid_val));
> 
> Instead of copying, couldn't you make the hypfs entry point
> into the array above, by using custom_runtime_set_var() here?

Hmm, probably yes.

> 
>> @@ -55,9 +74,12 @@ static int parse_pcid(const char *s)
>>           break;
>>       }
>>   
>> +    if ( !rc )
>> +        update_opt_pcid();
> 
> Personally I'd avoid the if() here - there's no harm updating
> the hypfs entry anyway.

Okay.

> 
>> --- a/xen/common/grant_table.c
>> +++ b/xen/common/grant_table.c
>> @@ -85,8 +85,10 @@ struct grant_table {
>>       struct grant_table_arch arch;
>>   };
>>   
>> -static int parse_gnttab_limit(const char *param, const char *arg,
>> -                              unsigned int *valp)
>> +#define GRANT_CUSTOM_VAL_SZ  12
>> +
>> +static int parse_gnttab_limit(const char *arg, unsigned int *valp,
>> +                              char *parval)
>>   {
>>       const char *e;
>>       unsigned long val;
>> @@ -99,28 +101,47 @@ static int parse_gnttab_limit(const char *param, const char *arg,
>>           return -ERANGE;
>>   
>>       *valp = val;
>> +    snprintf(parval, GRANT_CUSTOM_VAL_SZ, "%lu", val);
>>   
>>       return 0;
>>   }
>>   
>>   unsigned int __read_mostly opt_max_grant_frames = 64;
>> +static char __read_mostly opt_max_grant_frames_val[GRANT_CUSTOM_VAL_SZ];
>> +
>> +static void __init gnttab_max_frames_init(struct param_hypfs *par)
>> +{
>> +    custom_runtime_set_var(par, opt_max_grant_frames_val);
> 
> You still use a custom string buffer here. Can this "set-var"
> operation record that the variable (for presentation purposes)
> is simply of UINT type, handing a pointer to the actual
> variable?

No, this would result in the need to set a custom parameter via a
binary value passed in from user land. So I'd need to convert this
binary into a string to be parseable by the custom function.

> 
>> --- a/xen/common/hypfs.c
>> +++ b/xen/common/hypfs.c
>> @@ -10,6 +10,7 @@
>>   #include <xen/hypercall.h>
>>   #include <xen/hypfs.h>
>>   #include <xen/lib.h>
>> +#include <xen/param.h>
>>   #include <xen/rwlock.h>
>>   #include <public/hypfs.h>
>>   
>> @@ -281,6 +282,33 @@ int hypfs_write_bool(struct hypfs_entry_leaf *leaf,
>>       return 0;
>>   }
>>   
>> +int hypfs_write_custom(struct hypfs_entry_leaf *leaf,
>> +                       XEN_GUEST_HANDLE_PARAM(void) uaddr, unsigned long ulen)
>> +{
>> +    struct param_hypfs *p;
>> +    char *buf;
>> +    int ret;
>> +
>> +    buf = xzalloc_array(char, ulen);
>> +    if ( !buf )
>> +        return -ENOMEM;
>> +
>> +    ret = -EFAULT;
>> +    if ( copy_from_guest(buf, uaddr, ulen) )
>> +        goto out;
>> +
>> +    ret = -EDOM;
>> +    if ( !memchr(buf, 0, ulen) )
> 
> Once again " != buf + ulen - 1"? (EDOM also looks like an odd
> error code to use in this case, but I guess there's no really
> good one.)

" != buf + ulen - 1" is a logical choice with the change of patch 4.

> 
>> --- a/xen/drivers/char/console.c
>> +++ b/xen/drivers/char/console.c
>> @@ -75,12 +75,36 @@ enum con_timestamp_mode
>>       TSM_DATE_MS,       /* [YYYY-MM-DD HH:MM:SS.mmm] */
>>       TSM_BOOT,          /* [SSSSSS.uuuuuu] */
>>       TSM_RAW,           /* [XXXXXXXXXXXXXXXX] */
>> +    TSM_END
>> +};
>> +
>> +static const char *con_timestamp_mode_2_string[TSM_END] = {
>> +    [TSM_NONE] = "none",
>> +    [TSM_DATE] = "date",
>> +    [TSM_DATE_MS] = "datems",
>> +    [TSM_BOOT] = "boot",
>> +    [TSM_RAW] = "raw"
>>   };
>>   
>>   static enum con_timestamp_mode __read_mostly opt_con_timestamp_mode = TSM_NONE;
>> +static char con_timestamp_mode_val[7];
>> +
>> +static void update_con_timestamp_mode(void)
>> +{
>> +    strlcpy(con_timestamp_mode_val,
>> +            con_timestamp_mode_2_string[opt_con_timestamp_mode],
>> +            sizeof(con_timestamp_mode_val));
>> +}
>> +
>> +static void __init con_timestamp_mode_init(struct param_hypfs *par)
>> +{
>> +    custom_runtime_set_var(par, con_timestamp_mode_val);
>> +    update_con_timestamp_mode();
>> +}
>>   
>>   static int parse_console_timestamps(const char *s);
>> -custom_runtime_param("console_timestamps", parse_console_timestamps);
>> +custom_runtime_param("console_timestamps", parse_console_timestamps,
>> +                     con_timestamp_mode_init);
> 
> Same remark as for the PCID option, and then also for the log level
> ones further down. My main concern with how things are currently is
> that the amount of logic needed for custom params seems overly
> large.
> 
>> @@ -79,41 +88,94 @@ extern const struct kernel_param __param_start[], __param_end[];
>>             .type = OPT_IGNORE }
>>   
>>   #define __rtparam         __param(__dataparam)
>> +#define __paramfs         static __paramhypfs \
>> +    __attribute__((__aligned__(sizeof(void *)))) struct param_hypfs
>>   
>> -#define custom_runtime_only_param(_name, _var) \
>> +#define custom_runtime_set_var(parfs, var) \
>> +    { \
>> +        (parfs)->hypfs.write_ptr = &(var); \
>> +        (parfs)->hypfs.e.size = sizeof(var); \
> 
> All users of this use char[]. Why sizeof() rather than strlen(),

That is the maximum string length. Otherwise I wouldn't know I am
allowed to replace e.g. "on" by "noxpti".

> and why taking the address instead of enforcing this to be of
> (at least) array (potentially also "of char") type? Do you
> envision this to be needed for anything where the value isn't
> in string form, but still needs dynamically calculating? (As per
> above there may already be cases where non-string variables may
> want passing into here.)

Ah, this is a leftover from the failed experiment to allow other
types than strings. I'll change it accordingly.


Juergen

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