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Tue, 25 Aug 2026 07:20:56 -0700 (PDT) From: Ivy Lopez To: pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu Cc: alex@ghiti.fr, andrew.jones@oss.qualcomm.com, conor.dooley@microchip.com, schwab@suse.de, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Ivy Lopez Subject: [PATCH v2] riscv: hwprobe: fix has_fpu() to require D extension only Date: Tue, 25 Aug 2026 08:20:34 -0600 Message-ID: <20260825142034.31230-1-skunkolee@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260816003216.22534-1-skunkolee@gmail.com> References: <20260816003216.22534-1-skunkolee@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The kernel never supports F without D, since D depends on F. As such, has_fpu() checking either extension with '||' is incorrect: it reports FPU support when only F is present, which is not sufficient for D-dependent state save/restore, and weakens RISCV_HWPROBE_IMA_FD semantics to "F or D" instead of "F and D". Fix has_fpu() to check D only, which is equivalent to requiring both extensions given the dependency. Revert the explicit F && D check in sys_hwprobe.c back to calling has_fpu(), which is now correct. Link: https://bugzilla.kernel.org/show_bug.cgi?id=221874 Suggested-by: Conor Dooley Suggested-by: Andreas Schwab Signed-off-by: Ivy Lopez --- Changes in v2: - Original v1 approach (explicit F && D check in sys_hwprobe.c) was a no-op since F-without-D is structurally impossible. Per Conor and Andreas, fix has_fpu() itself instead, checking D only. Revert the sys_hwprobe.c change back to calling has_fpu(). - Link to v1: https://lore.kernel.org/r/20260816003216.22534-1-skunkolee@gmail.com arch/riscv/include/asm/switch_to.h | 4 ++-- arch/riscv/kernel/sys_hwprobe.c | 2 +- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h index 0e71eb82f920..8186cda88e17 100644 --- a/arch/riscv/include/asm/switch_to.h +++ b/arch/riscv/include/asm/switch_to.h @@ -60,8 +60,8 @@ static inline void __switch_to_fpu(struct task_struct *prev, static __always_inline bool has_fpu(void) { - return riscv_has_extension_likely(RISCV_ISA_EXT_f) || - riscv_has_extension_likely(RISCV_ISA_EXT_d); + /* D extension depends on F, so checking D alone is sufficient. */ + return riscv_has_extension_likely(RISCV_ISA_EXT_d); } #else static __always_inline bool has_fpu(void) { return false; } diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c index 7f91beb82a1c..1659d31fd288 100644 --- a/arch/riscv/kernel/sys_hwprobe.c +++ b/arch/riscv/kernel/sys_hwprobe.c @@ -85,7 +85,7 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe *pair, u64 missing = 0; pair->value = 0; - if (riscv_isa_extension_available(NULL, f) && riscv_isa_extension_available(NULL, d)) + if (has_fpu()) pair->value |= RISCV_HWPROBE_IMA_FD; if (riscv_isa_extension_available(NULL, c)) -- 2.55.0