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Wed, 26 Oct 2022 14:46:51 +0100 (BST) References: <20221006031113.1139454-1-richard.henderson@linaro.org> <20221006031113.1139454-23-richard.henderson@linaro.org> User-agent: mu4e 1.9.1; emacs 28.2.50 From: Alex =?utf-8?Q?Benn=C3=A9e?= To: Richard Henderson Cc: qemu-devel@nongnu.org, laurent@vivier.eu, pbonzini@redhat.com, imp@bsdimp.com, f4bug@amsat.org Subject: Re: [PATCH 22/24] accel/tcg: Use interval tree for user-only page tracking Date: Wed, 26 Oct 2022 14:36:35 +0100 In-reply-to: <20221006031113.1139454-23-richard.henderson@linaro.org> Message-ID: <87eduu4rzo.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=2a00:1450:4864:20::435; envelope-from=alex.bennee@linaro.org; helo=mail-wr1-x435.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Qemu-devel" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Richard Henderson writes: > Finish weaning user-only away from PageDesc. > > Using an interval tree to track page permissions means that > we can represent very large regions efficiently. > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/290 > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/967 > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1214 > Signed-off-by: Richard Henderson > --- > accel/tcg/internal.h | 4 +- > accel/tcg/tb-maint.c | 20 +- > accel/tcg/user-exec.c | 614 ++++++++++++++++++++++----------- > tests/tcg/multiarch/test-vma.c | 22 ++ > 4 files changed, 451 insertions(+), 209 deletions(-) > create mode 100644 tests/tcg/multiarch/test-vma.c > > diff --git a/accel/tcg/internal.h b/accel/tcg/internal.h > index 250f0daac9..c7e157d1cd 100644 > --- a/accel/tcg/internal.h > +++ b/accel/tcg/internal.h > @@ -24,9 +24,7 @@ > #endif >=20=20 > typedef struct PageDesc { > -#ifdef CONFIG_USER_ONLY > - unsigned long flags; > -#else > +#ifndef CONFIG_USER_ONLY > QemuSpin lock; > /* list of TBs intersecting this ram page */ > uintptr_t first_tb; > diff --git a/accel/tcg/tb-maint.c b/accel/tcg/tb-maint.c > index 14e8e47a6a..694440cb4a 100644 > --- a/accel/tcg/tb-maint.c > +++ b/accel/tcg/tb-maint.c > @@ -68,15 +68,23 @@ static void page_flush_tb(void) >=20=20 > int page_get_flags(target_ulong address) > { > - PageDesc *p; > + PageFlagsNode *p =3D pageflags_find(address, address); >=20=20 > - p =3D page_find(address >> TARGET_PAGE_BITS); > + /* > + * See util/interval-tree.c re lockless lookups: no false positives = but > + * there are false negatives. If we find nothing, retry with the mm= ap > + * lock acquired. > + */ > if (!p) { > - return 0; > + if (have_mmap_lock()) { > + return 0; > + } > + mmap_lock(); > + p =3D pageflags_find(address, address); > + mmap_unlock(); > + if (!p) { > + return 0; > + } > } > return p->flags; To avoid the brain twisting following locks and multiple return legs how ab= out this: int page_get_flags(target_ulong address) { PageFlagsNode *p =3D pageflags_find(address, address); /* * See util/interval-tree.c re lockless lookups: no false positives b= ut * there are false negatives. If we had the lock and found * nothing we are done, otherwise retry with the mmap lock acquired. */ if (have_mmap_lock()) { return p ? p->flags : 0; } mmap_lock(); p =3D pageflags_find(address, address); mmap_unlock(); return p ? p->flags : 0; } > diff --git a/tests/tcg/multiarch/test-vma.c b/tests/tcg/multiarch/test-vm= a.c > new file mode 100644 > index 0000000000..2893d60334 > --- /dev/null > +++ b/tests/tcg/multiarch/test-vma.c > @@ -0,0 +1,22 @@ > +/* > + * Test very large vma allocations. > + * The qemu out-of-memory condition was within the mmap syscall itself. > + * If the syscall actually returns with MAP_FAILED, the test succeeded. > + */ > +#include > + > +int main() > +{ > + int n =3D sizeof(size_t) =3D=3D 4 ? 32 : 45; > + > + for (int i =3D 28; i < n; i++) { > + size_t l =3D (size_t)1 << i; > + void *p =3D mmap(0, l, PROT_NONE, > + MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE, -1, = 0); > + if (p =3D=3D MAP_FAILED) { > + break; > + } > + munmap(p, l); > + } > + return 0; > +} So is the failure mode here we actually seg or bus out? --=20 Alex Benn=C3=A9e