Replace PAGE_OFFSET with KVM_HVA_ERR_BAD, to facilitate the cscope when
looking for where KVM_HVA_ERR_BAD is used.
Every time I use cscope to query the functions that are impacted by the
return value (KVM_HVA_ERR_BAD) of __gfn_to_hva_many(), I may miss
kvm_is_error_hva().
Signed-off-by: Dongli Zhang <[email protected]>
---
include/linux/kvm_host.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 7e7fd25b09b3..4dc0300e7766 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -143,7 +143,7 @@ static inline bool is_noslot_pfn(kvm_pfn_t pfn)
static inline bool kvm_is_error_hva(unsigned long addr)
{
- return addr >= PAGE_OFFSET;
+ return addr >= KVM_HVA_ERR_BAD;
}
#endif
--
2.34.1
On 1/03/2024 10:25 am, Dongli Zhang wrote:
> Replace PAGE_OFFSET with KVM_HVA_ERR_BAD, to facilitate the cscope when
> looking for where KVM_HVA_ERR_BAD is used.
>
> Every time I use cscope to query the functions that are impacted by the
> return value (KVM_HVA_ERR_BAD) of __gfn_to_hva_many(), I may miss
> kvm_is_error_hva().
I am not sure "to facilitate cscope" could be a justification to do some
code change in the kernel.
>
> Signed-off-by: Dongli Zhang <[email protected]>
> ---
> include/linux/kvm_host.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 7e7fd25b09b3..4dc0300e7766 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -143,7 +143,7 @@ static inline bool is_noslot_pfn(kvm_pfn_t pfn)
>
> static inline bool kvm_is_error_hva(unsigned long addr)
> {
> - return addr >= PAGE_OFFSET;
> + return addr >= KVM_HVA_ERR_BAD;
> }
>
> #endif
Also, IIUC the KVM_HVA_ERR_BAD _theoretically_ can be any random value
that can make kvm_is_error_hva() return false, while kvm_is_error_hva()
must catch all error HVAs.
E.g., if we ever change KVM_HVA_ERR_BAD to use any other value (although
I don't see why this could ever happen), then using KVM_HVA_ERR_BAD in
kvm_is_error_hva() would be broken.
In other words, it seems to me we should just use PAGE_OFFSET in
kvm_is_error_hva().
On 2/29/24 13:53, Huang, Kai wrote:
>
>
> On 1/03/2024 10:25 am, Dongli Zhang wrote:
>> Replace PAGE_OFFSET with KVM_HVA_ERR_BAD, to facilitate the cscope when
>> looking for where KVM_HVA_ERR_BAD is used.
>>
>> Every time I use cscope to query the functions that are impacted by the
>> return value (KVM_HVA_ERR_BAD) of __gfn_to_hva_many(), I may miss
>> kvm_is_error_hva().
>
> I am not sure "to facilitate cscope" could be a justification to do some code
> change in the kernel.
>
>>
>> Signed-off-by: Dongli Zhang <[email protected]>
>> ---
>> include/linux/kvm_host.h | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
>> index 7e7fd25b09b3..4dc0300e7766 100644
>> --- a/include/linux/kvm_host.h
>> +++ b/include/linux/kvm_host.h
>> @@ -143,7 +143,7 @@ static inline bool is_noslot_pfn(kvm_pfn_t pfn)
>> static inline bool kvm_is_error_hva(unsigned long addr)
>> {
>> - return addr >= PAGE_OFFSET;
>> + return addr >= KVM_HVA_ERR_BAD;
>> }
>> #endif
>
>
> Also, IIUC the KVM_HVA_ERR_BAD _theoretically_ can be any random value that can
> make kvm_is_error_hva() return false, while kvm_is_error_hva() must catch all
> error HVAs.
>
> E.g., if we ever change KVM_HVA_ERR_BAD to use any other value (although I don't
> see why this could ever happen), then using KVM_HVA_ERR_BAD in
> kvm_is_error_hva() would be broken.
>
> In other words, it seems to me we should just use PAGE_OFFSET in
> kvm_is_error_hva().
>
At least so far PAGE_OFFSET is the same value as KVM_HVA_ERR_BAD (except
mips/s390), as line 141. Therefore, this is "No functional change".
It indicates the userspace VMM can never have hva in the range of kernel space.
139 #ifndef KVM_HVA_ERR_BAD
140
141 #define KVM_HVA_ERR_BAD (PAGE_OFFSET)
142 #define KVM_HVA_ERR_RO_BAD (PAGE_OFFSET + PAGE_SIZE)
143
144 static inline bool kvm_is_error_hva(unsigned long addr)
145 {
146 return addr >= PAGE_OFFSET;
147 }
148
149 #endif
Regarding to "facilitate cscope", this happened since long time ago when I read
about ept_violation/mmio path.
1. The __gfn_to_hva_many() may return KVM_HVA_ERR_BAD for mmio.
2. Then I used cscope to find the location of KVM_HVA_ERR_BAD.
3. The kvm_is_error_hva() is not in the results.
4. It took me a while to figure out that the 'KVM_HVA_ERR_BAD' is indirectly
used by kvm_is_error_hva().
This is just based on my own experience when reading mmio code path. Thank you
very much!
Dongli Zhang
On 1/03/2024 11:13 am, Dongli Zhang wrote:
>
>
> On 2/29/24 13:53, Huang, Kai wrote:
>>
>>
>> On 1/03/2024 10:25 am, Dongli Zhang wrote:
>>> Replace PAGE_OFFSET with KVM_HVA_ERR_BAD, to facilitate the cscope when
>>> looking for where KVM_HVA_ERR_BAD is used.
>>>
>>> Every time I use cscope to query the functions that are impacted by the
>>> return value (KVM_HVA_ERR_BAD) of __gfn_to_hva_many(), I may miss
>>> kvm_is_error_hva().
>>
>> I am not sure "to facilitate cscope" could be a justification to do some code
>> change in the kernel.
>>
>>>
>>> Signed-off-by: Dongli Zhang <[email protected]>
>>> ---
>>> include/linux/kvm_host.h | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
>>> index 7e7fd25b09b3..4dc0300e7766 100644
>>> --- a/include/linux/kvm_host.h
>>> +++ b/include/linux/kvm_host.h
>>> @@ -143,7 +143,7 @@ static inline bool is_noslot_pfn(kvm_pfn_t pfn)
>>> static inline bool kvm_is_error_hva(unsigned long addr)
>>> {
>>> - return addr >= PAGE_OFFSET;
>>> + return addr >= KVM_HVA_ERR_BAD;
>>> }
>>> #endif
>>
>>
>> Also, IIUC the KVM_HVA_ERR_BAD _theoretically_ can be any random value that can
>> make kvm_is_error_hva() return false, while kvm_is_error_hva() must catch all
>> error HVAs.
>>
>> E.g., if we ever change KVM_HVA_ERR_BAD to use any other value (although I don't
>> see why this could ever happen), then using KVM_HVA_ERR_BAD in
>> kvm_is_error_hva() would be broken.
>>
>> In other words, it seems to me we should just use PAGE_OFFSET in
>> kvm_is_error_hva().
>>
>
>
> At least so far PAGE_OFFSET is the same value as KVM_HVA_ERR_BAD (except
> mips/s390), as line 141. Therefore, this is "No functional change".
>
> It indicates the userspace VMM can never have hva in the range of kernel space.
>
> 139 #ifndef KVM_HVA_ERR_BAD
> 140
> 141 #define KVM_HVA_ERR_BAD (PAGE_OFFSET)
> 142 #define KVM_HVA_ERR_RO_BAD (PAGE_OFFSET + PAGE_SIZE)
> 143
> 144 static inline bool kvm_is_error_hva(unsigned long addr)
> 145 {
> 146 return addr >= PAGE_OFFSET;
> 147 }
> 148
> 149 #endif
>
>
> Regarding to "facilitate cscope", this happened since long time ago when I read
> about ept_violation/mmio path.
>
> 1. The __gfn_to_hva_many() may return KVM_HVA_ERR_BAD for mmio.
> 2. Then I used cscope to find the location of KVM_HVA_ERR_BAD.
> 3. The kvm_is_error_hva() is not in the results.
> 4. It took me a while to figure out that the 'KVM_HVA_ERR_BAD' is indirectly
> used by kvm_is_error_hva().
>
> This is just based on my own experience when reading mmio code path. Thank you
> very much!
Neither of these can justify this patch.
As I replied earlier, _logically_, IIUC kvm_is_error_hva() shouldn't use
KVM_HVA_ERR_BAD, because the former needs to catch *ALL* bad HVA but the
latter could be some *RANDOM* bad HVA.