Re: [PATCH 18/18] KVM: arm64: Plumb the pKVM MMU in KVM

[Quentin Perret <qperret@google.com>]

On Tuesday 05 Nov 2024 at 13:53:22 (+0800), kernel test robot wrote:
> Hi Quentin,
> 
> kernel test robot noticed the following build warnings:
> 
> [auto build test WARNING on v6.12-rc6]
> [also build test WARNING on linus/master]
> [cannot apply to kvmarm/next next-20241104]
> [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/Quentin-Perret/KVM-arm64-Change-the-layout-of-enum-pkvm_page_state/20241104-213817
> base:   v6.12-rc6
> patch link:    https://lore.kernel.org/r/20241104133204.85208-19-qperret%40google.com
> patch subject: [PATCH 18/18] KVM: arm64: Plumb the pKVM MMU in KVM
> config: arm64-randconfig-002-20241105 (https://download.01.org/0day-ci/archive/20241105/202411051325.EBkzE0th-lkp@intel.com/config)
> compiler: aarch64-linux-gcc (GCC) 14.1.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241105/202411051325.EBkzE0th-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/202411051325.EBkzE0th-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
> >> arch/arm64/kvm/mmu.c:338: warning: Function parameter or struct member 'pgt' not described in 'kvm_s2_unmap'
> >> arch/arm64/kvm/mmu.c:338: warning: Function parameter or struct member 'addr' not described in 'kvm_s2_unmap'
> >> arch/arm64/kvm/mmu.c:338: warning: expecting prototype for __unmap_stage2_range(). Prototype was for kvm_s2_unmap() instead
> 
> 
> vim +338 arch/arm64/kvm/mmu.c
> 
>    299	
>    300	/*
>    301	 * Unmapping vs dcache management:
>    302	 *
>    303	 * If a guest maps certain memory pages as uncached, all writes will
>    304	 * bypass the data cache and go directly to RAM.  However, the CPUs
>    305	 * can still speculate reads (not writes) and fill cache lines with
>    306	 * data.
>    307	 *
>    308	 * Those cache lines will be *clean* cache lines though, so a
>    309	 * clean+invalidate operation is equivalent to an invalidate
>    310	 * operation, because no cache lines are marked dirty.
>    311	 *
>    312	 * Those clean cache lines could be filled prior to an uncached write
>    313	 * by the guest, and the cache coherent IO subsystem would therefore
>    314	 * end up writing old data to disk.
>    315	 *
>    316	 * This is why right after unmapping a page/section and invalidating
>    317	 * the corresponding TLBs, we flush to make sure the IO subsystem will
>    318	 * never hit in the cache.
>    319	 *
>    320	 * This is all avoided on systems that have ARM64_HAS_STAGE2_FWB, as
>    321	 * we then fully enforce cacheability of RAM, no matter what the guest
>    322	 * does.
>    323	 */
>    324	/**
>    325	 * __unmap_stage2_range -- Clear stage2 page table entries to unmap a range
>    326	 * @mmu:   The KVM stage-2 MMU pointer
>    327	 * @start: The intermediate physical base address of the range to unmap
>    328	 * @size:  The size of the area to unmap
>    329	 * @may_block: Whether or not we are permitted to block
>    330	 *
>    331	 * Clear a range of stage-2 mappings, lowering the various ref-counts.  Must
>    332	 * be called while holding mmu_lock (unless for freeing the stage2 pgd before
>    333	 * destroying the VM), otherwise another faulting VCPU may come in and mess
>    334	 * with things behind our backs.
>    335	 */
>    336	
>    337	static int kvm_s2_unmap(struct kvm_pgtable *pgt, u64 addr, u64 size)
>  > 338	{
>    339		return KVM_PGT_S2(unmap, pgt, addr, size);
>    340	}
>    341	

Oops, yes, that broke the kerneldoc comment, I'll fix in v2.