[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v2 07/10] arm/mm: Get rid of READ/WRITE_SYSREG32
On 27/04/2021 10:35, Michal Orzel wrote: AArch64 registers are 64bit whereas AArch32 registers are 32bit or 64bit. MSR/MRS are expecting 64bit values thus we should get rid of helpers READ/WRITE_SYSREG32 in favour of using READ/WRITE_SYSREG. We should also use register_t type when reading sysregs which can correspond to uint64_t or uint32_t. Even though many AArch64 registers have upper 32bit reserved it does not mean that they can't be widen in the future. Modify SCTLR_EL2 accesses to use READ/WRITE_SYSREG. SCTLR_EL2 already has bits defined in the range [32:63]. The ARM ARM defines them as unknown if implemented. This is a bit ambiguous. By writing in head.S SCTLR_EL2_SET we are zeroing the upper 32bit half which is correct but referring to this sysreg as 32bit is a latent bug because the top 32bit was not used by Xen. This seems to suggest the patch below will call SCTLR_EL2_SET whereas this is already existing code. Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx> --- Changes since v1: -Update commit message with SCTLR_EL2 analysis --- xen/arch/arm/mm.c | 2 +- xen/arch/arm/traps.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c index 59f8a3f15f..0e07335291 100644 --- a/xen/arch/arm/mm.c +++ b/xen/arch/arm/mm.c @@ -613,7 +613,7 @@ void __init remove_early_mappings(void) */ static void xen_pt_enforce_wnx(void) { - WRITE_SYSREG32(READ_SYSREG32(SCTLR_EL2) | SCTLR_Axx_ELx_WXN, SCTLR_EL2); + WRITE_SYSREG(READ_SYSREG(SCTLR_EL2) | SCTLR_Axx_ELx_WXN, SCTLR_EL2); /* * The TLBs may cache SCTLR_EL2.WXN. So ensure it is synchronized * before flushing the TLBs. diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c index c7acdb2087..e7384381cc 100644 --- a/xen/arch/arm/traps.c +++ b/xen/arch/arm/traps.c @@ -915,7 +915,7 @@ static void _show_registers(const struct cpu_user_regs *regs, printk(" VTTBR_EL2: %016"PRIx64"\n", ctxt->vttbr_el2); printk("\n");- printk(" SCTLR_EL2: %08"PRIx32"\n", READ_SYSREG32(SCTLR_EL2));+ printk(" SCTLR_EL2: %"PRIregister"\n", READ_SYSREG(SCTLR_EL2)); Your commit title suggests that you will modify mm.c but you are also modifying traps.c. So how about the following commit message: " xen/arm: Always access SCTLR_EL2 using {READ, WRITE}_SYSREG()The Armv8 specification describes the system register as a 64-bit value on AArch64 and 32-bit value on AArch32 (same as Armv7). Unfortunately, Xen is accessing the system registers using {READ, WRITE}_SYSREG32() which means the top 32-bit are clobbered. This is only a latent bug so far because Xen will not yet use the top 32-bit. There is also no change in behavior because arch/arm/arm64/head.S will initialize SCTLR_EL2 to a sane value with the top 32-bit zeroed. " Cheers, -- Julien Grall
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