linux-kernel - Re: [PATCH v9 3/8] x86/vmware: Introduce VMware hypercall API

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Message-ID: <20240511150225.GK2347895@kernel.org>
Date: Sat, 11 May 2024 16:02:25 +0100
From: Simon Horman <horms@...nel.org>
To: Alexey Makhalov <alexey.makhalov@...adcom.com>
Cc: linux-kernel@...r.kernel.org, virtualization@...ts.linux.dev,
	bp@...en8.de, hpa@...or.com, dave.hansen@...ux.intel.com,
	mingo@...hat.com, tglx@...utronix.de, x86@...nel.org,
	netdev@...r.kernel.org, richardcochran@...il.com,
	linux-input@...r.kernel.org, dmitry.torokhov@...il.com,
	zackr@...are.com, linux-graphics-maintainer@...are.com,
	pv-drivers@...are.com, timothym@...are.com, akaher@...are.com,
	dri-devel@...ts.freedesktop.org, daniel@...ll.ch, airlied@...il.com,
	tzimmermann@...e.de, mripard@...nel.org,
	maarten.lankhorst@...ux.intel.com, kirill.shutemov@...ux.intel.com,
	Nadav Amit <nadav.amit@...il.com>, Jeff Sipek <jsipek@...are.com>
Subject: Re: [PATCH v9 3/8] x86/vmware: Introduce VMware hypercall API

On Mon, May 06, 2024 at 02:53:00PM -0700, Alexey Makhalov wrote:
> Introduce vmware_hypercall family of functions. It is a common
> implementation to be used by the VMware guest code and virtual
> device drivers in architecture independent manner.
> 
> The API consists of vmware_hypercallX and vmware_hypercall_hb_{out,in}
> set of functions by analogy with KVM hypercall API. Architecture
> specific implementation is hidden inside.
> 
> It will simplify future enhancements in VMware hypercalls such
> as SEV-ES and TDX related changes without needs to modify a
> caller in device drivers code.
> 
> Current implementation extends an idea from commit bac7b4e84323
> ("x86/vmware: Update platform detection code for VMCALL/VMMCALL
> hypercalls") to have a slow, but safe path in VMWARE_HYPERCALL
> earlier during the boot when alternatives are not yet applied.
> This logic was inherited from VMWARE_CMD from the commit mentioned
> above. Default alternative code was optimized by size to reduce
> excessive nop alignment once alternatives are applied. Total
> default code size is 26 bytes, in worse case (3 bytes alternative)
> remaining 23 bytes will be aligned by only 3 long NOP instructions.
> 
> Signed-off-by: Alexey Makhalov <alexey.makhalov@...adcom.com>
> Reviewed-by: Nadav Amit <nadav.amit@...il.com>
> Reviewed-by: Jeff Sipek <jsipek@...are.com>

..

> diff --git a/arch/x86/include/asm/vmware.h b/arch/x86/include/asm/vmware.h

..

> +static inline
> +unsigned long vmware_hypercall3(unsigned long cmd, unsigned long in1,
> +				uint32_t *out1, uint32_t *out2)

nit: u32 is preferred over uint32_t.
     Likewise elsewhere in this patch-set.
..

>  /*
> - * The high bandwidth in call. The low word of edx is presumed to have the
> - * HB bit set.
> + * High bandwidth calls are not supported on encrypted memory guests.
> + * The caller should check cc_platform_has(CC_ATTR_MEM_ENCRYPT) and use
> + * low bandwidth hypercall it memory encryption is set.
> + * This assumption simplifies HB hypercall impementation to just I/O port

nit: implementation

     checkpatch.pl --codespell is your friend

> + * based approach without alternative patching.
>   */

..