linux-kernel - RE: [PATCH v2] x86/hyperv : Fixing removal of _

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Date:   Sun, 5 Nov 2023 15:25:29 +0000
From:   Michael Kelley <mhklinux@...look.com>
To:     Abhinav Singh <singhabhinav9051571833@...il.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "decui@...rosoft.com" <decui@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "haiyangz@...rosoft.com" <haiyangz@...rosoft.com>,
        "kys@...rosoft.com" <kys@...rosoft.com>,
        "niyelchu@...ux.microsoft.com" <niyelchu@...ux.microsoft.com>
Subject: RE: [PATCH v2] x86/hyperv : Fixing removal of __iomem address space
 warning

From: Abhinav Singh <singhabhinav9051571833@...il.com> Sent: Monday, October 30, 2023 3:50 PM
> 
> This patch fixes two sparse warnings
> 
> 1. sparse complaining about the removal of __iomem address
> space when casting the return value of this ioremap_cache(...)
> from `void __ioremap*` to `void*`.
> Fixed this by replacing the ioremap_cache(...)
> by memremap(...) and using MEMREMAP_DEC and MEMREMAP_WB flag for
> making
> sure the memory is always decrypted and it will support full write back
> cache.
> 
> 2. sparse complaining `expected void volatile [noderef] __iomem *addr`
> when calling iounmap with a non __iomem pointer.
> Fixed this by replacing iounmap(...) with memumap(...).
> 
> Signed-off-by: Abhinav Singh <singhabhinav9051571833@...il.com>

Since Nischala has posted her more comprehensive patch,
this patch can be dropped.  But see one comment below for
future reference.

> ---
> 
> v1:
> https://lore.kernel.org/all/19cec6f0-e176-4bcc-95a0-9d6eb0261ed1@gmail.com/T/
> 
> v1 to v2:
> 1. Fixed the comment which was earlier describing ioremap_cache(...).
> 2. Replaced iounmap(...) with memremap(...) inside function hv_cpu_die(...).
> 
>  arch/x86/hyperv/hv_init.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index 21556ad87f4b..2a14928b8a36 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -68,9 +68,11 @@ static int hyperv_init_ghcb(void)
>  	 */
>  	rdmsrl(MSR_AMD64_SEV_ES_GHCB, ghcb_gpa);
> 
> -	/* Mask out vTOM bit. ioremap_cache() maps decrypted */
> +	/* Mask out vTOM bit.
> +	MEMREMAP_WB full write back cache
> +	MEMREMAP_DEC maps decrypted memory */

This isn't the right style for multi-line patches.  Correct would be:

	/*
	 * Mask out vTOM bit.
	 * MEMREMAP_WB full write back cache
	 * MEMREMAP_DEC maps decrypted memory
	 */

Section 8 of coding-style.rst under Documentation/process covers
these details.   Note that the style is slightly different for code
under net and drivers/net.

Michael

>  	ghcb_gpa &= ~ms_hyperv.shared_gpa_boundary;
> -	ghcb_va = (void *)ioremap_cache(ghcb_gpa, HV_HYP_PAGE_SIZE);
> +	ghcb_va = memremap(ghcb_gpa, HV_HYP_PAGE_SIZE, MEMREMAP_WB | MEMREMAP_DEC);
>  	if (!ghcb_va)
>  		return -ENOMEM;
> 
> @@ -238,7 +240,7 @@ static int hv_cpu_die(unsigned int cpu)
>  	if (hv_ghcb_pg) {
>  		ghcb_va = (void **)this_cpu_ptr(hv_ghcb_pg);
>  		if (*ghcb_va)
> -			iounmap(*ghcb_va);
> +			memunmap(*ghcb_va);
>  		*ghcb_va = NULL;
>  	}
> 
> --
> 2.39.2