Re: [PATCH v3 8/9] arm64: KVM: implement lazy world switch for debug registers

Marc Zyngier
2014-07-09T11:18:33Z

On Wed, Jul 09 2014 at 10:45:05 am BST, Christoffer Dall <christoffer.dall@linaro.org> wrote:
> On Fri, Jun 20, 2014 at 02:00:06PM +0100, Marc Zyngier wrote:
>> Implement switching of the debug registers. While the number
>> of registers is massive, CPUs usually don't implement them all
>> (A57 has 6 breakpoints and 4 watchpoints, which gives us a total
>> of 22 registers "only").
>>
>> Also, we only save/restore them when MDSCR_EL1 has debug enabled,
>> or when we've flagged the debug registers as dirty. It means that
>> most of the time, we only save/restore MDSCR_EL1.
>>
>> Reviewed-by: Anup Patel <anup.patel@linaro.org>
>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>> ---
>> arch/arm64/kernel/asm-offsets.c | 1 +
>> arch/arm64/kvm/hyp.S | 462 +++++++++++++++++++++++++++++++++++++++-
>> 2 files changed, 457 insertions(+), 6 deletions(-)
>>

[...]

>> @@ -609,6 +1052,13 @@ __kvm_vcpu_return:
>>
>> bl __restore_sysregs
>> bl __restore_fpsimd
>> +
>> + skip_debug_state x3, 1f
>> + // Clear the dirty flag for the next run, as all the state has
>> + // already been saved.
>> + str xzr, [x0, #VCPU_DEBUG_FLAGS]
>> + bl __restore_debug
>> +1:
>> restore_host_regs
>>
>> mov x0, x1
>> --
>> 1.8.3.4
>>
>
> let's just try to remember the fact that we overwrite the entire bitmask
> here if we add more bits to that value some time:

I'll add a comment to that effect.

> Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>

Thanks!

M.
--
Without deviation from the norm, progress is not possible.