[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 3/6] x86/shadow: Use ERR_PTR infrastructure for sh_emulate_map_dest()
On 22/06/17 10:07, Jan Beulich wrote: >>>> On 22.06.17 at 10:21, <andrew.cooper3@xxxxxxxxxx> wrote: >> On 22/06/2017 09:14, Jan Beulich wrote: >>>>>> On 21.06.17 at 17:12, <andrew.cooper3@xxxxxxxxxx> wrote: >>>> sh_emulate_map_dest() predates the introduction of the generic ERR_PTR() >>>> infrasturcture, but take the opportunity to avoid opencoding it. >>>> >>>> The chosen error constants require need to be negative to work with >> IS_ERR(), >>>> but no other changes. >>> Drop one of "require" or "need"? >>> >>>> --- a/xen/arch/x86/mm/shadow/private.h >>>> +++ b/xen/arch/x86/mm/shadow/private.h >>>> @@ -395,10 +395,9 @@ void shadow_unhook_mappings(struct domain *d, mfn_t >> smfn, int user_only); >>>> >>>> /* Returns a mapped pointer to write to, or one of the following error >>>> * indicators. */ >>>> -#define MAPPING_UNHANDLEABLE ((void *)(unsigned long)X86EMUL_UNHANDLEABLE) >>>> -#define MAPPING_EXCEPTION ((void *)(unsigned long)X86EMUL_EXCEPTION) >>>> -#define MAPPING_SILENT_FAIL ((void *)(unsigned long)X86EMUL_OKAY) >>>> -#define sh_emulate_map_dest_failed(rc) ((unsigned long)(rc) <= 3) >>>> +#define MAPPING_UNHANDLEABLE ERR_PTR(~(long)X86EMUL_UNHANDLEABLE) >>>> +#define MAPPING_EXCEPTION ERR_PTR(~(long)X86EMUL_EXCEPTION) >>>> +#define MAPPING_SILENT_FAIL ERR_PTR(~(long)X86EMUL_OKAY) >>> While this doesn't change with your patch, this last definition has a >>> string dependency on X86EMUL_OKAY to be zero, yet there's no >>> respective BUILD_BUG_ON() anywhere. Would you mind adding >>> one at once? In any event >>> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> >> There is no longer any dependence on X86EMUL_OKAY being 0 (so far as I >> can see). All this logic would work fine if OKAY had the value 10 for >> example. > The mapping failure is "silent" only if X86EMUL_OKAY is zero, afaict. It is silent because MAPPING_SILENT_FAIL is considered an error by the caller (sh_x86_emulate_{write,cmpxchg}()), which unpacks the result (turning it into X86EMUL_OKAY) and passes it back into the emulation logic. This doesn't depend on the absolute value of X86EMUL_OKAY. > >> The only requirement (now) is that the X86EMUL constants are all within >> MAX_ERRNO so they count as errors as far as the ERR_PTR logic is >> concerned, and I suppose those should gain BUILD_BUG_ON()s > That would be helpful too. Its sadly not possible, as ERR_PTR() is a static inline and can't be evaluated in the context of BUILD_BUG_ON(). The best which is possible (without altering the errptr infrastructure) is BUILD_BUG_ON(IS_ERR_VALUE(~(long)X86EMUL_*)), but this won't catch a change which redefines the MAPPING_* constants. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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