* [Xen-devel] [PATCH] x86/vmx: Shrink TASK_SWITCH's hvm_task_switch_reason reasons[]
@ 2020-01-07 12:25 Andrew Cooper
2020-01-07 13:20 ` Jan Beulich
2020-01-19 4:09 ` Tian, Kevin
0 siblings, 2 replies; 3+ messages in thread
From: Andrew Cooper @ 2020-01-07 12:25 UTC (permalink / raw)
To: Xen-devel
Cc: Kevin Tian, Jan Beulich, Wei Liu, Andrew Cooper, Jun Nakajima,
Roger Pau Monné
No need to use 4-byte integers to store two bits of information.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wl@xen.org>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Jun Nakajima <jun.nakajima@intel.com>
CC: Kevin Tian <kevin.tian@intel.com>
---
xen/arch/x86/hvm/vmx/vmx.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index f83f102638..b79bca71ad 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -3978,7 +3978,7 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
vmx_update_cpu_exec_control(v);
break;
case EXIT_REASON_TASK_SWITCH: {
- static const enum hvm_task_switch_reason reasons[] = {
+ static const int8_t reasons[] = {
TSW_call_or_int, TSW_iret, TSW_jmp, TSW_call_or_int
};
unsigned int inst_len, source;
--
2.11.0
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^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [Xen-devel] [PATCH] x86/vmx: Shrink TASK_SWITCH's hvm_task_switch_reason reasons[]
2020-01-07 12:25 [Xen-devel] [PATCH] x86/vmx: Shrink TASK_SWITCH's hvm_task_switch_reason reasons[] Andrew Cooper
@ 2020-01-07 13:20 ` Jan Beulich
2020-01-19 4:09 ` Tian, Kevin
1 sibling, 0 replies; 3+ messages in thread
From: Jan Beulich @ 2020-01-07 13:20 UTC (permalink / raw)
To: Andrew Cooper
Cc: Xen-devel, Kevin Tian, Jun Nakajima, Wei Liu, Roger Pau Monné
On 07.01.2020 13:25, Andrew Cooper wrote:
> No need to use 4-byte integers to store two bits of information.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
In principle
Reviewed-by: Jan Beulich <jbeulich@suse.com>
But ...
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -3978,7 +3978,7 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
> vmx_update_cpu_exec_control(v);
> break;
> case EXIT_REASON_TASK_SWITCH: {
> - static const enum hvm_task_switch_reason reasons[] = {
> + static const int8_t reasons[] = {
> TSW_call_or_int, TSW_iret, TSW_jmp, TSW_call_or_int
> };
... given our general preference of unsigned types when values
can't become negative, why not uint8_t?
As an aside, elsewhere I saw people starting to convert code
because apparently gcc 10 will warn about enum type mismatches.
I didn't investigate yet whether that's just for enum -> enum
conversions, or also for enum <- / -> integer ones. Of course
it wouldn't be the end of the world if we had to revert the
change above; did you consider the alternative of making the
enum a __packed one (which would avoid potential issues like
the one named)?
Jan
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Xen-devel] [PATCH] x86/vmx: Shrink TASK_SWITCH's hvm_task_switch_reason reasons[]
2020-01-07 12:25 [Xen-devel] [PATCH] x86/vmx: Shrink TASK_SWITCH's hvm_task_switch_reason reasons[] Andrew Cooper
2020-01-07 13:20 ` Jan Beulich
@ 2020-01-19 4:09 ` Tian, Kevin
1 sibling, 0 replies; 3+ messages in thread
From: Tian, Kevin @ 2020-01-19 4:09 UTC (permalink / raw)
To: Andrew Cooper, Xen-devel
Cc: Nakajima, Jun, Wei Liu, Jan Beulich, Roger Pau Monné
> From: Andrew Cooper <andrew.cooper3@citrix.com>
> Sent: Tuesday, January 7, 2020 8:25 PM
>
> No need to use 4-byte integers to store two bits of information.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
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^ permalink raw reply [flat|nested] 3+ messages in thread
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2020-01-07 12:25 [Xen-devel] [PATCH] x86/vmx: Shrink TASK_SWITCH's hvm_task_switch_reason reasons[] Andrew Cooper
2020-01-07 13:20 ` Jan Beulich
2020-01-19 4:09 ` Tian, Kevin
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