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Re: [Xen-devel] [PATCH 03/11] x86: Initialise debug registers correctly
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Fri, 8 Jun 2018 16:23:25 +0100
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- Cc: Wei Liu <wei.liu2@xxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxx>
- Delivery-date: Fri, 08 Jun 2018 15:23:40 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 06/06/18 11:34, Roger Pau Monné wrote:
> On Mon, Jun 04, 2018 at 02:59:07PM +0100, Andrew Cooper wrote:
>> diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
>> index 528aff1..0872466 100644
>> --- a/xen/arch/x86/cpu/common.c
>> +++ b/xen/arch/x86/cpu/common.c
>> @@ -3,6 +3,7 @@
>> #include <xen/delay.h>
>> #include <xen/smp.h>
>> #include <asm/current.h>
>> +#include <asm/debugreg.h>
>> #include <asm/processor.h>
>> #include <asm/xstate.h>
>> #include <asm/msr.h>
>> @@ -823,10 +824,13 @@ void cpu_init(void)
>> /* Ensure FPU gets initialised for each domain. */
>> stts();
>>
>> - /* Clear all 6 debug registers: */
>> -#define CD(register) asm volatile ( "mov %0,%%db" #register : : "r"(0UL) );
>> - CD(0); CD(1); CD(2); CD(3); /* no db4 and db5 */; CD(6); CD(7);
>> -#undef CD
>> + /* Reset debug registers: */
>> + write_debugreg(0, 0);
>> + write_debugreg(1, 0);
>> + write_debugreg(2, 0);
>> + write_debugreg(3, 0);
>> + write_debugreg(6, X86_DR6_DEFAULT);
>> + write_debugreg(7, X86_DR7_DEFAULT);
> AFAICT you are writing the default init values, which should be there
> already. So this is just a safebelt in case the CPU is initialized
> with some bogus DR values?
Yes. Its just to sanitise state.
>> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
>> index c23983c..10415e6 100644
>> --- a/xen/arch/x86/hvm/hvm.c
>> +++ b/xen/arch/x86/hvm/hvm.c
>> @@ -40,6 +40,7 @@
>> #include <asm/shadow.h>
>> #include <asm/hap.h>
>> #include <asm/current.h>
>> +#include <asm/debugreg.h>
>> #include <asm/e820.h>
>> #include <asm/io.h>
>> #include <asm/regs.h>
>> @@ -3907,7 +3908,10 @@ void hvm_vcpu_reset_state(struct vcpu *v, uint16_t
>> cs, uint16_t ip)
>> v->arch.user_regs.rflags = X86_EFLAGS_MBS;
>> v->arch.user_regs.rdx = 0x00000f00;
>> v->arch.user_regs.rip = ip;
>> - memset(&v->arch.debugreg, 0, sizeof(v->arch.debugreg));
>> +
>> + memset(&v->arch.debugreg, 0, sizeof(v->arch.debugreg) - 16);
> For clarity I would use offsetof here, or rather just zero the whole
> thing. This is not a hot path, so I would prefer to avoid the
> optimization.
This particular expression doesn't survive past patch 6.
~Andrew
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