From: Alexandru Elisei <alexandru.elisei@arm.com> To: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, drjones@redhat.com Cc: eric.auger@redhat.com, andre.przywara@arm.com Subject: [kvm-unit-tests PATCH 03/10] arm/arm64: gic: Remove memory synchronization from ipi_clear_active_handler() Date: Wed, 25 Nov 2020 15:51:06 +0000 [thread overview] Message-ID: <20201125155113.192079-4-alexandru.elisei@arm.com> (raw) In-Reply-To: <20201125155113.192079-1-alexandru.elisei@arm.com> The gicv{2,3}-active test sends an IPI from the boot CPU to itself, then checks that the interrupt has been received as expected. There is no need to use inter-processor memory synchronization primitives on code that runs on the same CPU, so remove the unneeded memory barriers. The arrays are modified asynchronously (in the interrupt handler) and it is possible for the compiler to infer that they won't be changed during normal program flow and try to perform harmful optimizations (like stashing a previous read in a register and reusing it). To prevent this, for GICv2, the smp_wmb() in gicv2_ipi_send_self() is replaced with a compiler barrier. For GICv3, the wmb() barrier in gic_ipi_send_single() already implies a compiler barrier. Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com> --- arm/gic.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/arm/gic.c b/arm/gic.c index 401ffafe4299..4e947e8516a2 100644 --- a/arm/gic.c +++ b/arm/gic.c @@ -12,6 +12,7 @@ * This work is licensed under the terms of the GNU LGPL, version 2. */ #include <libcflat.h> +#include <linux/compiler.h> #include <errata.h> #include <asm/setup.h> #include <asm/processor.h> @@ -260,7 +261,8 @@ static void check_lpi_hits(int *expected, const char *msg) static void gicv2_ipi_send_self(void) { - smp_wmb(); + /* Prevent the compiler from optimizing memory accesses */ + barrier(); writel(2 << 24 | IPI_IRQ, gicv2_dist_base() + GICD_SGIR); } @@ -359,6 +361,7 @@ static struct gic gicv3 = { }, }; +/* Runs on the same CPU as the sender, no need for memory synchronization */ static void ipi_clear_active_handler(struct pt_regs *regs __unused) { u32 irqstat = gic_read_iar(); @@ -375,13 +378,10 @@ static void ipi_clear_active_handler(struct pt_regs *regs __unused) writel(val, base + GICD_ICACTIVER); - smp_rmb(); /* pairs with wmb in stats_reset */ ++acked[smp_processor_id()]; check_irqnr(irqnr); - smp_wmb(); /* pairs with rmb in check_acked */ } else { ++spurious[smp_processor_id()]; - smp_wmb(); } } -- 2.29.2
WARNING: multiple messages have this Message-ID (diff)
From: Alexandru Elisei <alexandru.elisei@arm.com> To: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, drjones@redhat.com Cc: andre.przywara@arm.com Subject: [kvm-unit-tests PATCH 03/10] arm/arm64: gic: Remove memory synchronization from ipi_clear_active_handler() Date: Wed, 25 Nov 2020 15:51:06 +0000 [thread overview] Message-ID: <20201125155113.192079-4-alexandru.elisei@arm.com> (raw) In-Reply-To: <20201125155113.192079-1-alexandru.elisei@arm.com> The gicv{2,3}-active test sends an IPI from the boot CPU to itself, then checks that the interrupt has been received as expected. There is no need to use inter-processor memory synchronization primitives on code that runs on the same CPU, so remove the unneeded memory barriers. The arrays are modified asynchronously (in the interrupt handler) and it is possible for the compiler to infer that they won't be changed during normal program flow and try to perform harmful optimizations (like stashing a previous read in a register and reusing it). To prevent this, for GICv2, the smp_wmb() in gicv2_ipi_send_self() is replaced with a compiler barrier. For GICv3, the wmb() barrier in gic_ipi_send_single() already implies a compiler barrier. Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com> --- arm/gic.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/arm/gic.c b/arm/gic.c index 401ffafe4299..4e947e8516a2 100644 --- a/arm/gic.c +++ b/arm/gic.c @@ -12,6 +12,7 @@ * This work is licensed under the terms of the GNU LGPL, version 2. */ #include <libcflat.h> +#include <linux/compiler.h> #include <errata.h> #include <asm/setup.h> #include <asm/processor.h> @@ -260,7 +261,8 @@ static void check_lpi_hits(int *expected, const char *msg) static void gicv2_ipi_send_self(void) { - smp_wmb(); + /* Prevent the compiler from optimizing memory accesses */ + barrier(); writel(2 << 24 | IPI_IRQ, gicv2_dist_base() + GICD_SGIR); } @@ -359,6 +361,7 @@ static struct gic gicv3 = { }, }; +/* Runs on the same CPU as the sender, no need for memory synchronization */ static void ipi_clear_active_handler(struct pt_regs *regs __unused) { u32 irqstat = gic_read_iar(); @@ -375,13 +378,10 @@ static void ipi_clear_active_handler(struct pt_regs *regs __unused) writel(val, base + GICD_ICACTIVER); - smp_rmb(); /* pairs with wmb in stats_reset */ ++acked[smp_processor_id()]; check_irqnr(irqnr); - smp_wmb(); /* pairs with rmb in check_acked */ } else { ++spurious[smp_processor_id()]; - smp_wmb(); } } -- 2.29.2 _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
next prev parent reply other threads:[~2020-11-25 15:50 UTC|newest] Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-11-25 15:51 [kvm-unit-tests PATCH 00/10] GIC fixes and improvements Alexandru Elisei 2020-11-25 15:51 ` Alexandru Elisei 2020-11-25 15:51 ` [kvm-unit-tests PATCH 01/10] lib: arm/arm64: gicv3: Add missing barrier when sending IPIs Alexandru Elisei 2020-11-25 15:51 ` Alexandru Elisei 2020-12-01 16:37 ` Auger Eric 2020-12-01 16:37 ` Auger Eric 2020-12-01 17:37 ` Alexandru Elisei 2020-12-01 17:37 ` Alexandru Elisei 2020-11-25 15:51 ` [kvm-unit-tests PATCH 02/10] lib: arm/arm64: gicv2: " Alexandru Elisei 2020-11-25 15:51 ` Alexandru Elisei 2020-12-01 16:37 ` Auger Eric 2020-12-01 16:37 ` Auger Eric 2020-11-25 15:51 ` Alexandru Elisei [this message] 2020-11-25 15:51 ` [kvm-unit-tests PATCH 03/10] arm/arm64: gic: Remove memory synchronization from ipi_clear_active_handler() Alexandru Elisei 2020-12-01 16:37 ` Auger Eric 2020-12-01 16:37 ` Auger Eric 2020-12-02 14:02 ` Alexandru Elisei 2020-12-02 14:02 ` Alexandru Elisei 2020-12-02 14:14 ` Alexandru Elisei 2020-12-02 14:14 ` Alexandru Elisei 2020-12-03 9:41 ` Auger Eric 2020-12-03 9:41 ` Auger Eric 2020-11-25 15:51 ` [kvm-unit-tests PATCH 04/10] arm/arm64: gic: Remove unnecessary synchronization with stats_reset() Alexandru Elisei 2020-11-25 15:51 ` Alexandru Elisei 2020-12-01 16:48 ` Auger Eric 2020-12-01 16:48 ` Auger Eric 2020-12-02 14:06 ` Alexandru Elisei 2020-12-02 14:06 ` Alexandru Elisei 2020-12-03 13:10 ` Auger Eric 2020-12-03 13:10 ` Auger Eric 2020-11-25 15:51 ` [kvm-unit-tests PATCH 05/10] arm/arm64: gic: Use correct memory ordering for the IPI test Alexandru Elisei 2020-11-25 15:51 ` Alexandru Elisei 2020-12-03 13:10 ` Auger Eric 2020-12-03 13:10 ` Auger Eric 2020-12-03 13:21 ` Alexandru Elisei 2020-12-03 13:21 ` Alexandru Elisei 2020-11-25 15:51 ` [kvm-unit-tests PATCH 06/10] arm/arm64: gic: Check spurious and bad_sender in the active test Alexandru Elisei 2020-11-25 15:51 ` Alexandru Elisei 2020-12-03 13:10 ` Auger Eric 2020-12-03 13:10 ` Auger Eric 2020-11-25 15:51 ` [kvm-unit-tests PATCH 07/10] arm/arm64: gic: Wait for writes to acked or spurious to complete Alexandru Elisei 2020-11-25 15:51 ` Alexandru Elisei 2020-12-03 13:21 ` Auger Eric 2020-12-03 13:21 ` Auger Eric 2020-11-25 15:51 ` [kvm-unit-tests PATCH 08/10] arm/arm64: gic: Split check_acked() into two functions Alexandru Elisei 2020-11-25 15:51 ` Alexandru Elisei 2020-12-03 13:39 ` Auger Eric 2020-12-03 13:39 ` Auger Eric 2020-12-10 14:45 ` Alexandru Elisei 2020-12-10 14:45 ` Alexandru Elisei 2020-12-15 13:58 ` Auger Eric 2020-12-15 13:58 ` Auger Eric 2020-12-16 11:40 ` Alexandru Elisei 2020-12-16 11:40 ` Alexandru Elisei 2020-12-16 12:37 ` Auger Eric 2020-12-16 12:37 ` Auger Eric 2020-11-25 15:51 ` [kvm-unit-tests PATCH 09/10] arm/arm64: gic: Make check_acked() more generic Alexandru Elisei 2020-11-25 15:51 ` Alexandru Elisei 2020-12-03 14:59 ` Auger Eric 2020-12-03 14:59 ` Auger Eric 2020-11-25 15:51 ` [kvm-unit-tests PATCH 10/10] arm64: gic: Use IPI test checking for the LPI tests Alexandru Elisei 2020-11-25 15:51 ` Alexandru Elisei 2020-11-26 9:30 ` Zenghui Yu 2020-11-26 9:30 ` Zenghui Yu 2020-11-27 14:50 ` Alexandru Elisei 2020-11-27 14:50 ` Alexandru Elisei 2020-11-30 13:59 ` Zenghui Yu 2020-11-30 13:59 ` Zenghui Yu 2020-11-30 14:19 ` Alexandru Elisei 2020-11-30 14:19 ` Alexandru Elisei 2020-12-01 15:09 ` Alexandru Elisei 2020-12-01 15:09 ` Alexandru Elisei 2020-11-30 17:48 ` Auger Eric 2020-11-30 17:48 ` Auger Eric 2020-12-03 14:59 ` Auger Eric 2020-12-03 14:59 ` Auger Eric 2020-12-09 10:29 ` Alexandru Elisei 2020-12-09 10:29 ` Alexandru Elisei
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