From b698e4eef5111e2df7598261b09dcef8249b7ae6 Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Tue, 7 May 2019 12:55:02 +0100 Subject: arm: Allow system registers for KVM guests to be changed by QEMU code At the moment the Arm implementations of kvm_arch_{get,put}_registers() don't support having QEMU change the values of system registers (aka coprocessor registers for AArch32). This is because although kvm_arch_get_registers() calls write_list_to_cpustate() to update the CPU state struct fields (so QEMU code can read the values in the usual way), kvm_arch_put_registers() does not call write_cpustate_to_list(), meaning that any changes to the CPU state struct fields will not be passed back to KVM. The rationale for this design is documented in a comment in the AArch32 kvm_arch_put_registers() -- writing the values in the cpregs list into the CPU state struct is "lossy" because the write of a register might not succeed, and so if we blindly copy the CPU state values back again we will incorrectly change register values for the guest. The assumption was that no QEMU code would need to write to the registers. However, when we implemented debug support for KVM guests, we broke that assumption: the code to handle "set the guest up to take a breakpoint exception" does so by updating various guest registers including ESR_EL1. Support this by making kvm_arch_put_registers() synchronize CPU state back into the list. We sync only those registers where the initial write succeeds, which should be sufficient. This commit is the same as commit 823e1b3818f9b10b824ddc which we had to revert in commit 942f99c825fc94c8b1a4, except that the bug which was preventing EDK2 guest firmware running has been fixed: kvm_arm_reset_vcpu() now calls write_list_to_cpustate(). Signed-off-by: Peter Maydell Reviewed-by: Richard Henderson Tested-by: Eric Auger --- target/arm/cpu.h | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) (limited to 'target/arm/cpu.h') diff --git a/target/arm/cpu.h b/target/arm/cpu.h index 22bc6e00ab..0304ddd9f1 100644 --- a/target/arm/cpu.h +++ b/target/arm/cpu.h @@ -2610,18 +2610,25 @@ bool write_list_to_cpustate(ARMCPU *cpu); /** * write_cpustate_to_list: * @cpu: ARMCPU + * @kvm_sync: true if this is for syncing back to KVM * * For each register listed in the ARMCPU cpreg_indexes list, write * its value from the ARMCPUState structure into the cpreg_values list. * This is used to copy info from TCG's working data structures into * KVM or for outbound migration. * + * @kvm_sync is true if we are doing this in order to sync the + * register state back to KVM. In this case we will only update + * values in the list if the previous list->cpustate sync actually + * successfully wrote the CPU state. Otherwise we will keep the value + * that is in the list. + * * Returns: true if all register values were read correctly, * false if some register was unknown or could not be read. * Note that we do not stop early on failure -- we will attempt * reading all registers in the list. */ -bool write_cpustate_to_list(ARMCPU *cpu); +bool write_cpustate_to_list(ARMCPU *cpu, bool kvm_sync); #define ARM_CPUID_TI915T 0x54029152 #define ARM_CPUID_TI925T 0x54029252 -- cgit v1.2.3-55-g7522