Re: [PATCH 1/3] KVM: Support sharing gpc locks

kernel test robot
2023-01-28T21:43:52Z

Hi David,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on kvm/queue]
[also build test ERROR on linus/master v6.2-rc5 next-20230127]
[cannot apply to kvm/linux-next]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url: https://github.com/intel-lab-lkp/linux/commits/David-Stevens/KVM-Support-sharing-gpc-locks/20230128-161425
base: https://git.kernel.org/pub/scm/virt/kvm/kvm.git queue
patch link: https://lore.kernel.org/r/20230127044500.680329-2-stevensd%40google.com
patch subject: [PATCH 1/3] KVM: Support sharing gpc locks
config: i386-randconfig-a003 (https://download.01.org/0day-ci/archive/20230129/202301290541.8nmbLtFC-lkp@intel.com/config)
compiler: gcc-11 (Debian 11.3.0-8) 11.3.0
reproduce (this is a W=1 build):
# https://github.com/intel-lab-lkp/linux/commit/14d62b317199184bb71256cc5f652b04fb2f9107
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review David-Stevens/KVM-Support-sharing-gpc-locks/20230128-161425
git checkout 14d62b317199184bb71256cc5f652b04fb2f9107
# save the config file
mkdir build_dir && cp config build_dir/.config
make W=1 O=build_dir ARCH=i386 olddefconfig
make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash arch/x86/ drivers/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

arch/x86/kvm/xen.c: In function 'kvm_xen_update_runstate_guest':
>> arch/x86/kvm/xen.c:319:45: error: 'gpc1->lock' is a pointer; did you mean to use '->'?
319 | lock_set_subclass(gpc1->lock.dep_map, 1, _THIS_IP_);
| ^
| ->

vim +319 arch/x86/kvm/xen.c

172
173 static void kvm_xen_update_runstate_guest(struct kvm_vcpu *v, bool atomic)
174 {
175 struct kvm_vcpu_xen *vx = &v->arch.xen;
176 struct gfn_to_pfn_cache *gpc1 = &vx->runstate_cache;
177 struct gfn_to_pfn_cache *gpc2 = &vx->runstate2_cache;
178 size_t user_len, user_len1, user_len2;
179 struct vcpu_runstate_info rs;
180 unsigned long flags;
181 size_t times_ofs;
182 uint8_t *update_bit = NULL;
183 uint64_t entry_time;
184 uint64_t *rs_times;
185 int *rs_state;
186
187 /*
188 * The only difference between 32-bit and 64-bit versions of the
189 * runstate struct is the alignment of uint64_t in 32-bit, which
190 * means that the 64-bit version has an additional 4 bytes of
191 * padding after the first field 'state'. Let's be really really
192 * paranoid about that, and matching it with our internal data
193 * structures that we memcpy into it...
194 */
195 BUILD_BUG_ON(offsetof(struct vcpu_runstate_info, state) != 0);
196 BUILD_BUG_ON(offsetof(struct compat_vcpu_runstate_info, state) != 0);
197 BUILD_BUG_ON(sizeof(struct compat_vcpu_runstate_info) != 0x2c);
198 #ifdef CONFIG_X86_64
199 /*
200 * The 64-bit structure has 4 bytes of padding before 'state_entry_time'
201 * so each subsequent field is shifted by 4, and it's 4 bytes longer.
202 */
203 BUILD_BUG_ON(offsetof(struct vcpu_runstate_info, state_entry_time) !=
204 offsetof(struct compat_vcpu_runstate_info, state_entry_time) + 4);
205 BUILD_BUG_ON(offsetof(struct vcpu_runstate_info, time) !=
206 offsetof(struct compat_vcpu_runstate_info, time) + 4);
207 BUILD_BUG_ON(sizeof(struct vcpu_runstate_info) != 0x2c + 4);
208 #endif
209 /*
210 * The state field is in the same place at the start of both structs,
211 * and is the same size (int) as vx->current_runstate.
212 */
213 BUILD_BUG_ON(offsetof(struct vcpu_runstate_info, state) !=
214 offsetof(struct compat_vcpu_runstate_info, state));
215 BUILD_BUG_ON(sizeof_field(struct vcpu_runstate_info, state) !=
216 sizeof(vx->current_runstate));
217 BUILD_BUG_ON(sizeof_field(struct compat_vcpu_runstate_info, state) !=
218 sizeof(vx->current_runstate));
219
220 /*
221 * The state_entry_time field is 64 bits in both versions, and the
222 * XEN_RUNSTATE_UPDATE flag is in the top bit, which given that x86
223 * is little-endian means that it's in the last *byte* of the word.
224 * That detail is important later.
225 */
226 BUILD_BUG_ON(sizeof_field(struct vcpu_runstate_info, state_entry_time) !=
227 sizeof(uint64_t));
228 BUILD_BUG_ON(sizeof_field(struct compat_vcpu_runstate_info, state_entry_time) !=
229 sizeof(uint64_t));
230 BUILD_BUG_ON((XEN_RUNSTATE_UPDATE >> 56) != 0x80);
231
232 /*
233 * The time array is four 64-bit quantities in both versions, matching
234 * the vx->runstate_times and immediately following state_entry_time.
235 */
236 BUILD_BUG_ON(offsetof(struct vcpu_runstate_info, state_entry_time) !=
237 offsetof(struct vcpu_runstate_info, time) - sizeof(uint64_t));
238 BUILD_BUG_ON(offsetof(struct compat_vcpu_runstate_info, state_entry_time) !=
239 offsetof(struct compat_vcpu_runstate_info, time) - sizeof(uint64_t));
240 BUILD_BUG_ON(sizeof_field(struct vcpu_runstate_info, time) !=
241 sizeof_field(struct compat_vcpu_runstate_info, time));
242 BUILD_BUG_ON(sizeof_field(struct vcpu_runstate_info, time) !=
243 sizeof(vx->runstate_times));
244
245 if (IS_ENABLED(CONFIG_64BIT) && v->kvm->arch.xen.long_mode) {
246 user_len = sizeof(struct vcpu_runstate_info);
247 times_ofs = offsetof(struct vcpu_runstate_info,
248 state_entry_time);
249 } else {
250 user_len = sizeof(struct compat_vcpu_runstate_info);
251 times_ofs = offsetof(struct compat_vcpu_runstate_info,
252 state_entry_time);
253 }
254
255 /*
256 * There are basically no alignment constraints. The guest can set it
257 * up so it crosses from one page to the next, and at arbitrary byte
258 * alignment (and the 32-bit ABI doesn't align the 64-bit integers
259 * anyway, even if the overall struct had been 64-bit aligned).
260 */
261 if ((gpc1->gpa & ~PAGE_MASK) + user_len >= PAGE_SIZE) {
262 user_len1 = PAGE_SIZE - (gpc1->gpa & ~PAGE_MASK);
263 user_len2 = user_len - user_len1;
264 } else {
265 user_len1 = user_len;
266 user_len2 = 0;
267 }
268 BUG_ON(user_len1 + user_len2 != user_len);
269
270 retry:
271 /*
272 * Attempt to obtain the GPC lock on *both* (if there are two)
273 * gfn_to_pfn caches that cover the region.
274 */
275 if (atomic) {
276 local_irq_save(flags);
277 if (!read_trylock(gpc1->lock)) {
278 local_irq_restore(flags);
279 return;
280 }
281 } else {
282 read_lock_irqsave(gpc1->lock, flags);
283 }
284 while (!kvm_gpc_check(gpc1, user_len1)) {
285 read_unlock_irqrestore(gpc1->lock, flags);
286
287 /* When invoked from kvm_sched_out() we cannot sleep */
288 if (atomic)
289 return;
290
291 if (kvm_gpc_refresh(gpc1, user_len1))
292 return;
293
294 read_lock_irqsave(gpc1->lock, flags);
295 }
296
297 if (likely(!user_len2)) {
298 /*
299 * Set up three pointers directly to the runstate_info
300 * struct in the guest (via the GPC).
301 *
302 * • @rs_state → state field
303 * • @rs_times → state_entry_time field.
304 * • @update_bit → last byte of state_entry_time, which
305 * contains the XEN_RUNSTATE_UPDATE bit.
306 */
307 rs_state = gpc1->khva;
308 rs_times = gpc1->khva + times_ofs;
309 if (v->kvm->arch.xen.runstate_update_flag)
310 update_bit = ((void *)(&rs_times[1])) - 1;
311 } else {
312 /*
313 * The guest's runstate_info is split across two pages and we
314 * need to hold and validate both GPCs simultaneously. We can
315 * declare a lock ordering GPC1 > GPC2 because nothing else
316 * takes them more than one at a time. Set a subclass on the
317 * gpc1 lock to make lockdep shut up about it.
318 */
> 319 lock_set_subclass(gpc1->lock.dep_map, 1, _THIS_IP_);
320 if (atomic) {
321 if (!read_trylock(gpc2->lock)) {
322 read_unlock_irqrestore(gpc1->lock, flags);
323 return;
324 }
325 } else {
326 read_lock(gpc2->lock);
327 }
328
329 if (!kvm_gpc_check(gpc2, user_len2)) {
330 read_unlock(gpc2->lock);
331 read_unlock_irqrestore(gpc1->lock, flags);
332
333 /* When invoked from kvm_sched_out() we cannot sleep */
334 if (atomic)
335 return;
336
337 /*
338 * Use kvm_gpc_activate() here because if the runstate
339 * area was configured in 32-bit mode and only extends
340 * to the second page now because the guest changed to
341 * 64-bit mode, the second GPC won't have been set up.
342 */
343 if (kvm_gpc_activate(gpc2, gpc1->gpa + user_len1,
344 user_len2))
345 return;
346
347 /*
348 * We dropped the lock on GPC1 so we have to go all the
349 * way back and revalidate that too.
350 */
351 goto retry;
352 }
353
354 /*
355 * In this case, the runstate_info struct will be assembled on
356 * the kernel stack (compat or not as appropriate) and will
357 * be copied to GPC1/GPC2 with a dual memcpy. Set up the three
358 * rs pointers accordingly.
359 */
360 rs_times = &rs.state_entry_time;
361
362 /*
363 * The rs_state pointer points to the start of what we'll
364 * copy to the guest, which in the case of a compat guest
365 * is the 32-bit field that the compiler thinks is padding.
366 */
367 rs_state = ((void *)rs_times) - times_ofs;
368
369 /*
370 * The update_bit is still directly in the guest memory,
371 * via one GPC or the other.
372 */
373 if (v->kvm->arch.xen.runstate_update_flag) {
374 if (user_len1 >= times_ofs + sizeof(uint64_t))
375 update_bit = gpc1->khva + times_ofs +
376 sizeof(uint64_t) - 1;
377 else
378 update_bit = gpc2->khva + times_ofs +
379 sizeof(uint64_t) - 1 - user_len1;
380 }
381

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