[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 3/4] x86/HVM: implement memory read caching
> -----Original Message----- > From: Jan Beulich [mailto:JBeulich@xxxxxxxx] > Sent: 12 September 2018 09:38 > To: Paul Durrant <Paul.Durrant@xxxxxxxxxx> > Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; George Dunlap > <George.Dunlap@xxxxxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>; xen-devel > <xen-devel@xxxxxxxxxxxxxxxxxxxx> > Subject: RE: [PATCH v2 3/4] x86/HVM: implement memory read caching > > >>> On 11.09.18 at 18:20, <Paul.Durrant@xxxxxxxxxx> wrote: > >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx] > >> Sent: 11 September 2018 14:15 > >> > >> @@ -2664,9 +2685,35 @@ void hvm_dump_emulation_state(const char > >> hvmemul_ctxt->insn_buf); > >> } > >> > >> +struct hvmemul_cache *hvmemul_cache_init(unsigned int nents) > >> +{ > >> + struct hvmemul_cache *cache = xmalloc_bytes(offsetof(struct > >> hvmemul_cache, > >> + ents[nents])); > >> + > >> + if ( cache ) > >> + { > >> + cache->num_ents = 0; > >> + cache->max_ents = nents; > >> + } > >> + > >> + return cache; > >> +} > >> + > >> bool hvmemul_read_cache(const struct hvmemul_cache *cache, > paddr_t > >> gpa, > >> unsigned int level, void *buffer, unsigned int > >> size) > >> { > >> + unsigned int i; > >> + > > > > Here you could return false if cache is NULL... > > This one could perhaps be considered, but ... > > >> @@ -2674,6 +2721,35 @@ void hvmemul_write_cache(struct hvmemul_ > >> unsigned int level, const void *buffer, > >> unsigned int size) > >> { > >> + unsigned int i; > >> + > > > > ...and here just bail out. Thus making both functions safe to call with a > > NULL cache. > > ... I'm pretty much opposed to this: The term "cache" might be slightly > confusing here, but I lack a better idea for a name. Its presence is > required for correctness. After all the series is not a performance > improvement, but a plain bug fix (generalizing what we were able to > special case for the actually observed problem in commit 91afb8139f > ["x86/HVM: suppress I/O completion for port output"]). And with > that I'd rather leave the read side as is as well. > Ok. I have no strong objection to the code structure as it stands so you can add my R-b to this and patch #2. Paul > Jan > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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