From: Palmer Dabbelt <palmer@sifive.com> To: linux-riscv@lists.infradead.org, Paul Walmsley <paul.walmsley@sifive.com>, marco@decred.org, me@carlosedp.com, joel@sing.id.au Cc: linux-kernel@vger.kernel.org, Palmer Dabbelt <palmer@sifive.com> Subject: [PATCH] RISC-V: Break load reservations during switch_to Date: Wed, 5 Jun 2019 16:17:35 -0700 [thread overview] Message-ID: <20190605231735.26581-1-palmer@sifive.com> (raw) The comment describes why in detail. This was found because QEMU never gives up load reservations, the issue is unlikely to manifest on real hardware. Thanks to Carlos Eduardo for finding the bug! Signed-off-by: Palmer Dabbelt <palmer@sifive.com> --- arch/riscv/kernel/entry.S | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S index 1c1ecc238cfa..e9fc3480e6b4 100644 --- a/arch/riscv/kernel/entry.S +++ b/arch/riscv/kernel/entry.S @@ -330,6 +330,24 @@ ENTRY(__switch_to) add a3, a0, a4 add a4, a1, a4 REG_S ra, TASK_THREAD_RA_RA(a3) + /* + * The Linux ABI allows programs to depend on load reservations being + * broken on context switches, but the ISA doesn't require that the + * hardware ever breaks a load reservation. The only way to break a + * load reservation is with a store conditional, so we emit one here. + * Since nothing ever takes a load reservation on TASK_THREAD_RA_RA we + * know this will always fail, but just to be on the safe side this + * writes the same value that was unconditionally written by the + * previous instruction. + */ +#if (TASK_THREAD_RA_RA != 0) +# error "The offset between ra and ra is non-zero" +#endif +#if (__riscv_xlen == 64) + sc.d x0, ra, 0(a3) +#else + sc.w x0, ra, 0(a3) +#endif REG_S sp, TASK_THREAD_SP_RA(a3) REG_S s0, TASK_THREAD_S0_RA(a3) REG_S s1, TASK_THREAD_S1_RA(a3) -- 2.21.0
WARNING: multiple messages have this Message-ID (diff)
From: Palmer Dabbelt <palmer@sifive.com> To: linux-riscv@lists.infradead.org, Paul Walmsley <paul.walmsley@sifive.com>, marco@decred.org, me@carlosedp.com, joel@sing.id.au Cc: Palmer Dabbelt <palmer@sifive.com>, linux-kernel@vger.kernel.org Subject: [PATCH] RISC-V: Break load reservations during switch_to Date: Wed, 5 Jun 2019 16:17:35 -0700 [thread overview] Message-ID: <20190605231735.26581-1-palmer@sifive.com> (raw) The comment describes why in detail. This was found because QEMU never gives up load reservations, the issue is unlikely to manifest on real hardware. Thanks to Carlos Eduardo for finding the bug! Signed-off-by: Palmer Dabbelt <palmer@sifive.com> --- arch/riscv/kernel/entry.S | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S index 1c1ecc238cfa..e9fc3480e6b4 100644 --- a/arch/riscv/kernel/entry.S +++ b/arch/riscv/kernel/entry.S @@ -330,6 +330,24 @@ ENTRY(__switch_to) add a3, a0, a4 add a4, a1, a4 REG_S ra, TASK_THREAD_RA_RA(a3) + /* + * The Linux ABI allows programs to depend on load reservations being + * broken on context switches, but the ISA doesn't require that the + * hardware ever breaks a load reservation. The only way to break a + * load reservation is with a store conditional, so we emit one here. + * Since nothing ever takes a load reservation on TASK_THREAD_RA_RA we + * know this will always fail, but just to be on the safe side this + * writes the same value that was unconditionally written by the + * previous instruction. + */ +#if (TASK_THREAD_RA_RA != 0) +# error "The offset between ra and ra is non-zero" +#endif +#if (__riscv_xlen == 64) + sc.d x0, ra, 0(a3) +#else + sc.w x0, ra, 0(a3) +#endif REG_S sp, TASK_THREAD_SP_RA(a3) REG_S s0, TASK_THREAD_S0_RA(a3) REG_S s1, TASK_THREAD_S1_RA(a3) -- 2.21.0 _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv
next reply other threads:[~2019-06-05 23:18 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-06-05 23:17 Palmer Dabbelt [this message] 2019-06-05 23:17 ` [PATCH] RISC-V: Break load reservations during switch_to Palmer Dabbelt 2019-06-06 8:37 ` Marco Peereboom 2019-06-06 8:37 ` Marco Peereboom 2019-06-06 9:05 ` Christoph Hellwig 2019-06-06 9:05 ` Christoph Hellwig 2019-06-06 19:10 ` Palmer Dabbelt 2019-06-06 19:10 ` Palmer Dabbelt 2019-06-06 19:32 ` Andreas Schwab 2019-06-06 19:32 ` Andreas Schwab 2019-06-07 22:12 ` Palmer Dabbelt 2019-06-07 22:12 ` Palmer Dabbelt
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