* Re: [PATCH v6 1/2] kvm: sev: Add SEV-SNP guest request throttling
[not found] <20250605150236.3775954-2-dionnaglaze@google.com>
@ 2025-06-06 9:58 ` kernel test robot
0 siblings, 0 replies; only message in thread
From: kernel test robot @ 2025-06-06 9:58 UTC (permalink / raw)
To: Dionna Glaze, kvm, linux-kernel
Cc: llvm, oe-kbuild-all, linux-coco, Dionna Glaze, Thomas Lendacky,
Paolo Bonzini, Joerg Roedel, Peter Gonda, Borislav Petkov,
Sean Christopherson
Hi Dionna,
kernel test robot noticed the following build warnings:
[auto build test WARNING on mst-vhost/linux-next]
[also build test WARNING on linus/master v6.15 next-20250606]
[cannot apply to kvm/queue kvm/next 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/Dionna-Glaze/kvm-sev-Add-SEV-SNP-guest-request-throttling/20250605-230536
base: https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git linux-next
patch link: https://lore.kernel.org/r/20250605150236.3775954-2-dionnaglaze%40google.com
patch subject: [PATCH v6 1/2] kvm: sev: Add SEV-SNP guest request throttling
config: x86_64-rhel-9.4-rust (https://download.01.org/0day-ci/archive/20250606/202506061922.q7OljdiN-lkp@intel.com/config)
compiler: clang version 18.1.8 (https://github.com/llvm/llvm-project 3b5b5c1ec4a3095ab096dd780e84d7ab81f3d7ff)
rustc: rustc 1.78.0 (9b00956e5 2024-04-29)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250606/202506061922.q7OljdiN-lkp@intel.com/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202506061922.q7OljdiN-lkp@intel.com/
All warnings (new ones prefixed by >>):
>> arch/x86/kvm/svm/sev.c:376:6: warning: variable 'throttle_interval' set but not used [-Wunused-but-set-variable]
376 | u64 throttle_interval;
| ^
1 warning generated.
vim +/throttle_interval +376 arch/x86/kvm/svm/sev.c
334
335 /*
336 * This sets up bounce buffers/firmware pages to handle SNP Guest Request
337 * messages (e.g. attestation requests). See "SNP Guest Request" in the GHCB
338 * 2.0 specification for more details.
339 *
340 * Technically, when an SNP Guest Request is issued, the guest will provide its
341 * own request/response pages, which could in theory be passed along directly
342 * to firmware rather than using bounce pages. However, these pages would need
343 * special care:
344 *
345 * - Both pages are from shared guest memory, so they need to be protected
346 * from migration/etc. occurring while firmware reads/writes to them. At a
347 * minimum, this requires elevating the ref counts and potentially needing
348 * an explicit pinning of the memory. This places additional restrictions
349 * on what type of memory backends userspace can use for shared guest
350 * memory since there is some reliance on using refcounted pages.
351 *
352 * - The response page needs to be switched to Firmware-owned[1] state
353 * before the firmware can write to it, which can lead to potential
354 * host RMP #PFs if the guest is misbehaved and hands the host a
355 * guest page that KVM might write to for other reasons (e.g. virtio
356 * buffers/etc.).
357 *
358 * Both of these issues can be avoided completely by using separately-allocated
359 * bounce pages for both the request/response pages and passing those to
360 * firmware instead. So that's what is being set up here.
361 *
362 * Guest requests rely on message sequence numbers to ensure requests are
363 * issued to firmware in the order the guest issues them, so concurrent guest
364 * requests generally shouldn't happen. But a misbehaved guest could issue
365 * concurrent guest requests in theory, so a mutex is used to serialize
366 * access to the bounce buffers.
367 *
368 * [1] See the "Page States" section of the SEV-SNP Firmware ABI for more
369 * details on Firmware-owned pages, along with "RMP and VMPL Access Checks"
370 * in the APM for details on the related RMP restrictions.
371 */
372 static int snp_guest_req_init(struct kvm *kvm)
373 {
374 struct kvm_sev_info *sev = to_kvm_sev_info(kvm);
375 struct page *req_page;
> 376 u64 throttle_interval;
377
378 req_page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
379 if (!req_page)
380 return -ENOMEM;
381
382 sev->guest_resp_buf = snp_alloc_firmware_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
383 if (!sev->guest_resp_buf) {
384 __free_page(req_page);
385 return -EIO;
386 }
387
388 sev->guest_req_buf = page_address(req_page);
389 mutex_init(&sev->guest_req_mutex);
390
391 throttle_interval = ((u64)sev_snp_request_ratelimit_khz * HZ) / HZ_PER_KHZ;
392 ratelimit_state_init(&sev->snp_guest_msg_rs, sev_snp_request_ratelimit_khz, 1);
393
394 return 0;
395 }
396
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