linux-kernel - Re: [PATCH v2 07/21] arm64: KVM: VHE: Patch out kern_hyp

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Message-ID: <56AF5FF1.4010701@arm.com>
Date:	Mon, 1 Feb 2016 13:38:57 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Christoffer Dall <christoffer.dall@...aro.org>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu
Subject: Re: [PATCH v2 07/21] arm64: KVM: VHE: Patch out kern_hyp_va

On 01/02/16 13:20, Christoffer Dall wrote:
> On Mon, Jan 25, 2016 at 03:53:41PM +0000, Marc Zyngier wrote:
>> The kern_hyp_va macro is pretty meaninless with VHE, as there is
>> only one mapping - the kernel one.
>>
>> In order to keep the code readable and efficient, use runtime
>> patching to replace the 'and' instruction used to compute the VA
>> with a 'nop'.
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
>> ---
>>  arch/arm64/include/asm/kvm_mmu.h | 11 ++++++++++-
>>  arch/arm64/kvm/hyp/hyp.h         | 25 ++++++++++++++++++++++---
>>  2 files changed, 32 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
>> index d3e6d7b..62f0d14 100644
>> --- a/arch/arm64/include/asm/kvm_mmu.h
>> +++ b/arch/arm64/include/asm/kvm_mmu.h
>> @@ -23,13 +23,16 @@
>>  #include <asm/cpufeature.h>
>>  
>>  /*
>> - * As we only have the TTBR0_EL2 register, we cannot express
>> + * As ARMv8.0 only has the TTBR0_EL2 register, we cannot express
>>   * "negative" addresses. This makes it impossible to directly share
>>   * mappings with the kernel.
>>   *
>>   * Instead, give the HYP mode its own VA region at a fixed offset from
>>   * the kernel by just masking the top bits (which are all ones for a
>>   * kernel address).
>> + *
>> + * ARMv8.1 (using VHE) does have a TTBR1_EL2, and doesn't use these
>> + * macros (the entire kernel runs at EL2).
>>   */
>>  #define HYP_PAGE_OFFSET_SHIFT	VA_BITS
>>  #define HYP_PAGE_OFFSET_MASK	((UL(1) << HYP_PAGE_OFFSET_SHIFT) - 1)
>> @@ -56,6 +59,8 @@
>>  
>>  #ifdef __ASSEMBLY__
>>  
>> +#include <asm/alternative.h>
>> +#include <asm/cpufeature.h>
>>  #include <asm/kvm_arm.h>
>>  
>>  .macro setup_vtcr tmp1, tmp2
>> @@ -84,7 +89,11 @@
>>   * reg: VA to be converted.
>>   */
>>  .macro kern_hyp_va	reg
>> +alternative_if_not ARM64_HAS_VIRT_HOST_EXTN	
>>  	and	\reg, \reg, #HYP_PAGE_OFFSET_MASK
>> +alternative_else
>> +	nop
>> +alternative_endif
>>  .endm
>>  
>>  #else
>> diff --git a/arch/arm64/kvm/hyp/hyp.h b/arch/arm64/kvm/hyp/hyp.h
>> index fb27517..fc502f3 100644
>> --- a/arch/arm64/kvm/hyp/hyp.h
>> +++ b/arch/arm64/kvm/hyp/hyp.h
>> @@ -25,9 +25,28 @@
>>  
>>  #define __hyp_text __section(.hyp.text) notrace
>>  
>> -#define kern_hyp_va(v) (typeof(v))((unsigned long)(v) & HYP_PAGE_OFFSET_MASK)
>> -#define hyp_kern_va(v) (typeof(v))((unsigned long)(v) - HYP_PAGE_OFFSET \
>> -						      + PAGE_OFFSET)
>> +static inline unsigned long __kern_hyp_va(unsigned long v)
>> +{
>> +	asm volatile(ALTERNATIVE("and %0, %0, %1",
>> +				 "nop",
>> +				 ARM64_HAS_VIRT_HOST_EXTN)
>> +		     : "+r" (v) : "i" (HYP_PAGE_OFFSET_MASK));
>> +	return v;
>> +}
>> +
>> +#define kern_hyp_va(v) (typeof(v))(__kern_hyp_va((unsigned long)(v)))
>> +
>> +static inline unsigned long __hyp_kern_va(unsigned long v)
>> +{
>> +	u64 offset = PAGE_OFFSET - HYP_PAGE_OFFSET;
>> +	asm volatile(ALTERNATIVE("add %0, %0, %1",
>> +				 "nop",
>> +				 ARM64_HAS_VIRT_HOST_EXTN)
>> +		     : "+r" (v) : "r" (offset));
>> +	return v;
>> +}
>> +
>> +#define hyp_kern_va(v) (typeof(v))(__hyp_kern_va((unsigned long)(v)))
> 
> why do we need this casting of values instead of just defining these
> inlines and calling them directly with proper typing?

We commonly pass both pointers and unsigned long to this helper. Do you
really want a separate helper for each type instead of one that does it all?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...