linux-kernel - Re: [PATCH 2/2] KVM: selftests: Test forced instruction emulation in dirty log test (x86 only)

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Message-ID: <Zc6d6fwakreoVtN5@linux.dev>
Date: Thu, 15 Feb 2024 15:27:37 -0800
From: Oliver Upton <oliver.upton@...ux.dev>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, David Matlack <dmatlack@...gle.com>,
	Pasha Tatashin <tatashin@...gle.com>,
	Michael Krebs <mkrebs@...gle.com>
Subject: Re: [PATCH 2/2] KVM: selftests: Test forced instruction emulation in
 dirty log test (x86 only)

On Thu, Feb 15, 2024 at 01:33:48PM -0800, Sean Christopherson wrote:

[...]

> +/* TODO: Expand this madness to also support u8, u16, and u32 operands. */
> +#define vcpu_arch_put_guest(mem, val, rand) 						\
> +do {											\
> +	if (!is_forced_emulation_enabled || !(rand & 1)) {				\
> +		*mem = val;								\
> +	} else if (rand & 2) {								\
> +		__asm__ __volatile__(KVM_FEP "movq %1, %0"				\
> +				     : "+m" (*mem)					\
> +				     : "r" (val) : "memory");				\
> +	} else {									\
> +		uint64_t __old = READ_ONCE(*mem);					\
> +											\
> +		__asm__ __volatile__(KVM_FEP LOCK_PREFIX "cmpxchgq %[new], %[ptr]"	\
> +				     : [ptr] "+m" (*mem), [old] "+a" (__old)		\
> +				     : [new]"r" (val) : "memory", "cc");		\
> +	}										\
> +} while (0)
> +

Last bit of bikeshedding then I'll go... Can you just use a C function
and #define it so you can still do ifdeffery to slam in a default
implementation?

I hate macros :)

-- 
Thanks,
Oliver