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([2804:14c:482:92eb:ffdf:6b35:b94d:258]) by smtp.gmail.com with ESMTPSA id j21sm18004462pjz.26.2021.07.19.22.37.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 19 Jul 2021 22:37:58 -0700 (PDT) Message-ID: <283e44591010dcb0690769afaef147add3b36978.camel@gmail.com> Subject: Re: [PATCH v5 02/11] powerpc/kernel/iommu: Add new iommu_table_in_use() helper From: Leonardo =?ISO-8859-1?Q?Br=E1s?= To: Frederic Barrat , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Alexey Kardashevskiy , David Gibson , kernel test robot , Nicolin Chen Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Date: Tue, 20 Jul 2021 02:38:16 -0300 In-Reply-To: <29c199f3-63a8-3edb-b29e-de157431d89f@linux.ibm.com> References: <20210716082755.428187-1-leobras.c@gmail.com> <20210716082755.428187-3-leobras.c@gmail.com> <29c199f3-63a8-3edb-b29e-de157431d89f@linux.ibm.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.40.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Fred, thanks for this feedback! Sorry if I miss anything, this snippet was written for v1 over an year ago, and I have not taken a look at it ever since. On Mon, 2021-07-19 at 15:53 +0200, Frederic Barrat wrote: > > > On 16/07/2021 10:27, Leonardo Bras wrote: > > @@ -1099,18 +1105,13 @@ int iommu_take_ownership(struct iommu_table > > *tbl) > >         for (i = 0; i < tbl->nr_pools; i++) > >                 spin_lock_nest_lock(&tbl->pools[i].lock, &tbl- > > >large_pool.lock); > >   > > -       iommu_table_release_pages(tbl); > > - > > -       if (!bitmap_empty(tbl->it_map, tbl->it_size)) { > > +       if (iommu_table_in_use(tbl)) { > >                 pr_err("iommu_tce: it_map is not empty"); > >                 ret = -EBUSY; > > -               /* Undo iommu_table_release_pages, i.e. restore > > bit#0, etc */ > > -               iommu_table_reserve_pages(tbl, tbl- > > >it_reserved_start, > > -                               tbl->it_reserved_end); > > -       } else { > > -               memset(tbl->it_map, 0xff, sz); > >         } > >   > > +       memset(tbl->it_map, 0xff, sz); > > + > > > So if the table is not empty, we fail (EBUSY) but we now also > completely > overwrite the bitmap. It was in an unexpected state, but we're making > it > worse. Or am I missing something? IIRC there was a reason to do that at the time, but TBH I don't really remember it, and by looking at the code right now you seem to be correct about this causing trouble. I will send a v6 fixing it soon. Please review the remaining patches for some issue I may be missing. Alexey, any comments on that? > >    Fred > Again, thank you for reviewing Fred! Best regards, Leonardo Bras