From: Peter Maydell Date: Fri, 14 Nov 2025 15:53:04 +0000 (+0000) Subject: hw/arm/armv7m: Disable reentrancy guard for v7m_sysreg_ns_ops MRs X-Git-Tag: v10.2.0-rc2~8^2~1 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=4a934d284dfac9fa19b0f47874f12d9b3519c21c;p=thirdparty%2Fqemu.git hw/arm/armv7m: Disable reentrancy guard for v7m_sysreg_ns_ops MRs For M-profile cores which support TrustZone, there are some memory areas which are "NS aliases" -- a Secure access to these addresses really performs an NS access to a different part of the device. We implement these using MemoryRegionOps read and write functions which pass the access on with adjusted attributes using memory_region_dispatch_read() and memory_region_dispatch_write(). Since the MR we are dispatching to is owned by the same device that owns the NS-alias MR (the TYPE_ARMV7M container object), this trips the reentrancy-guard that is applied by access_with_adjusted_size(). Mark the NS alias MemoryRegions as disable_reentrancy_guard; this is safe because v7m_sysreg_ns_read() and v7m_sysreg_ns_write() do not touch any of the device's state. (Any further reentrancy attempts by the underlying MR will still be caught.) Without this fix, an attempt to read from an address like 0xe002e010, which is a register in the NS systick alias, will fail and provoke qemu-system-arm: warning: Blocked re-entrant IO on MemoryRegion: v7m_systick at addr: 0x0 We didn't notice this earlier because almost all code accesses the registers and systick via the non-alias addresses; the NS aliases are only need for the rarer case of Secure code that needs to manage the NS timer or system state on behalf of NS code. Note that although the v7m_systick_ops read and write functions also call memory_region_dispatch_{read,write}, this MR does not need to have the reentrancy-guard disabled because the underlying MR that it forwards to is owned by a different device (the TYPE_SYSTICK timer device). Reported via a stackoverflow question: https://stackoverflow.com/questions/79808107/what-this-error-is-even-about-qemu-system-arm-warning-blocked-re-entrant-io Cc: qemu-stable@nongnu.org Signed-off-by: Peter Maydell Reviewed-by: Philippe Mathieu-Daudé Message-id: 20251114155304.2662414-1-peter.maydell@linaro.org --- diff --git a/hw/arm/armv7m.c b/hw/arm/armv7m.c index c4a9c3ac52..7fa1b37630 100644 --- a/hw/arm/armv7m.c +++ b/hw/arm/armv7m.c @@ -442,6 +442,12 @@ static void armv7m_realize(DeviceState *dev, Error **errp) &v7m_sysreg_ns_ops, sysbus_mmio_get_region(sbd, 0), "nvic_sysregs_ns", 0x1000); + /* + * This MR calls memory_region_dispatch_read/write to access the + * real region for the NVIC sysregs (which is also owned by this + * device), so reentrancy through here is expected and safe. + */ + s->sysreg_ns_mem.disable_reentrancy_guard = true; memory_region_add_subregion(&s->container, 0xe002e000, &s->sysreg_ns_mem); } @@ -499,6 +505,12 @@ static void armv7m_realize(DeviceState *dev, Error **errp) memory_region_init_io(&s->systick_ns_mem, OBJECT(s), &v7m_sysreg_ns_ops, &s->systickmem, "v7m_systick_ns", 0xe0); + /* + * This MR calls memory_region_dispatch_read/write to access the + * real region for the systick regs (which is also owned by this + * device), so reentrancy through here is expected and safe. + */ + s->systick_ns_mem.disable_reentrancy_guard = true; memory_region_add_subregion_overlap(&s->container, 0xe002e010, &s->systick_ns_mem, 1); }