[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v4 1/5] x86/HVM: split restore state checking from state loading
On Mon, Dec 18, 2023 at 03:39:55PM +0100, Jan Beulich wrote: > ..., at least as reasonably feasible without making a check hook > mandatory (in particular strict vs relaxed/zero-extend length checking > can't be done early this way). > > Note that only one of the two uses of "real" hvm_load() is accompanied > with a "checking" one. The other directly consumes hvm_save() output, > which ought to be well-formed. This means that while input data related > checks don't need repeating in the "load" function when already done by > the "check" one (albeit assertions to this effect may be desirable), > domain state related checks (e.g. has_xyz(d)) will be required in both > places. > > Suggested-by: Roger Pau Monné <roger.pau@xxxxxxxxxx> > Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx> > --- > Now that this re-arranges hvm_load() anyway, wouldn't it be better to > down the vCPU-s ahead of calling arch_hvm_load() (which is now easy to > arrange for)? Seems OK to me. > Do we really need all the copying involved in use of _hvm_read_entry() > (backing hvm_load_entry()? Zero-extending loads are likely easier to > handle that way, but for strict loads all we gain is a reduced risk of > unaligned accesses (compared to simply pointing into h->data[]). I do feel it's safer to copy the data so the checks are done against what's loaded. Albeit hvm_load() is already using hvm_get_entry(). > --- > v4: Fold hvm_check() into hvm_load(). > v2: New. > > --- a/xen/arch/x86/domctl.c > +++ b/xen/arch/x86/domctl.c > @@ -379,8 +379,12 @@ long arch_do_domctl( > if ( copy_from_guest(c.data, domctl->u.hvmcontext.buffer, c.size) != > 0 ) > goto sethvmcontext_out; > > + ret = hvm_load(d, false, &c); > + if ( ret ) > + goto sethvmcontext_out; > + > domain_pause(d); > - ret = hvm_load(d, &c); > + ret = hvm_load(d, true, &c); Now that the check has been done ahead, do we want to somehow assert that this cannot fail? AIUI that's the expectation. > domain_unpause(d); > > sethvmcontext_out: > --- a/xen/arch/x86/hvm/hvm.c > +++ b/xen/arch/x86/hvm/hvm.c > @@ -5397,7 +5397,7 @@ int hvm_copy_context_and_params(struct d > } > > c.cur = 0; > - rc = hvm_load(dst, &c); > + rc = hvm_load(dst, true, &c); > > out: > vfree(c.data); > --- a/xen/arch/x86/hvm/save.c > +++ b/xen/arch/x86/hvm/save.c > @@ -30,7 +30,8 @@ static void arch_hvm_save(struct domain > d->arch.hvm.sync_tsc = rdtsc(); > } > > -static int arch_hvm_load(struct domain *d, const struct hvm_save_header *hdr) > +static int arch_hvm_check(const struct domain *d, > + const struct hvm_save_header *hdr) > { > uint32_t eax, ebx, ecx, edx; > > @@ -55,6 +56,11 @@ static int arch_hvm_load(struct domain * > "(%#"PRIx32") and restored on another (%#"PRIx32").\n", > d->domain_id, hdr->cpuid, eax); > > + return 0; > +} > + > +static void arch_hvm_load(struct domain *d, const struct hvm_save_header > *hdr) > +{ > /* Restore guest's preferred TSC frequency. */ > if ( hdr->gtsc_khz ) > d->arch.tsc_khz = hdr->gtsc_khz; > @@ -66,13 +72,12 @@ static int arch_hvm_load(struct domain * > > /* VGA state is not saved/restored, so we nobble the cache. */ > d->arch.hvm.stdvga.cache = STDVGA_CACHE_DISABLED; > - > - return 0; > } > > /* List of handlers for various HVM save and restore types */ > static struct { > hvm_save_handler save; > + hvm_check_handler check; > hvm_load_handler load; > const char *name; > size_t size; > @@ -88,6 +93,7 @@ void __init hvm_register_savevm(uint16_t > { > ASSERT(typecode <= HVM_SAVE_CODE_MAX); > ASSERT(hvm_sr_handlers[typecode].save == NULL); > + ASSERT(hvm_sr_handlers[typecode].check == NULL); > ASSERT(hvm_sr_handlers[typecode].load == NULL); > hvm_sr_handlers[typecode].save = save_state; > hvm_sr_handlers[typecode].load = load_state; > @@ -275,12 +281,10 @@ int hvm_save(struct domain *d, hvm_domai > return 0; > } > > -int hvm_load(struct domain *d, hvm_domain_context_t *h) > +int hvm_load(struct domain *d, bool real, hvm_domain_context_t *h) Maybe the 'real' parameter should instead be an enum: enum hvm_load_action { CHECK, LOAD, }; int hvm_load(struct domain *d, enum hvm_load_action action, hvm_domain_context_t *h); Otherwise a comment might be warranted about how 'real' affects the logic in the function. > { > const struct hvm_save_header *hdr; > struct hvm_save_descriptor *desc; > - hvm_load_handler handler; > - struct vcpu *v; > int rc; > > if ( d->is_dying ) > @@ -291,50 +295,91 @@ int hvm_load(struct domain *d, hvm_domai > if ( !hdr ) > return -ENODATA; > > - rc = arch_hvm_load(d, hdr); > - if ( rc ) > - return rc; > + rc = arch_hvm_check(d, hdr); Shouldn't this _check function only be called when real == false? > + if ( real ) > + { > + struct vcpu *v; > + > + ASSERT(!rc); > + arch_hvm_load(d, hdr); > > - /* Down all the vcpus: we only re-enable the ones that had state saved. > */ > - for_each_vcpu(d, v) > - if ( !test_and_set_bit(_VPF_down, &v->pause_flags) ) > - vcpu_sleep_nosync(v); > + /* > + * Down all the vcpus: we only re-enable the ones that had state > + * saved. > + */ > + for_each_vcpu(d, v) > + if ( !test_and_set_bit(_VPF_down, &v->pause_flags) ) > + vcpu_sleep_nosync(v); > + } > + else if ( rc ) > + return rc; > > for ( ; ; ) > { > + const char *name; > + hvm_load_handler load; > + > if ( h->size - h->cur < sizeof(struct hvm_save_descriptor) ) > { > /* Run out of data */ > printk(XENLOG_G_ERR > "HVM%d restore: save did not end with a null entry\n", > d->domain_id); > + ASSERT(!real); > return -ENODATA; > } > > /* Read the typecode of the next entry and check for the end-marker > */ > desc = (struct hvm_save_descriptor *)(&h->data[h->cur]); > - if ( desc->typecode == 0 ) > + if ( desc->typecode == HVM_SAVE_CODE(END) ) > + { > + /* Reset cursor for hvm_load(, true, ). */ > + if ( !real ) > + h->cur = 0; > return 0; > + } > > /* Find the handler for this entry */ > - if ( (desc->typecode > HVM_SAVE_CODE_MAX) || > - ((handler = hvm_sr_handlers[desc->typecode].load) == NULL) ) > + if ( desc->typecode >= ARRAY_SIZE(hvm_sr_handlers) || > + !(name = hvm_sr_handlers[desc->typecode].name) || > + !(load = hvm_sr_handlers[desc->typecode].load) ) > { > printk(XENLOG_G_ERR "HVM%d restore: unknown entry typecode %u\n", > d->domain_id, desc->typecode); The message is not very accurate here, it does fail when the typecode is unknown, but also fails when such typecode has no name or load function setup. Thanks, Roger.
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