Re: [PATCH v2] x86/hyperv : Fixing removal of __iomem address space warning

[Abhinav Singh]

On 11/5/23 20:55, Michael Kelley wrote:
> From: Abhinav Singh <singhabhinav9051571833@xxxxxxxxx> 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@xxxxxxxxx>
>
> 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@xxxxxxxxx/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
Thanks a lot for taking a look and the suggestion, will keep this in 
mind in future patches.

Thanks,
Abhinav