Re: [PATCH 2/2] virtio: replace arch_has_restricted_virtio_memory_access()

[Juergen Gross via Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>]

On 27.04.22 16:09, Tom Lendacky wrote:
> On 4/27/22 07:37, Juergen Gross wrote:
> > On 27.04.22 14:28, Borislav Petkov wrote:
> > > On Wed, Apr 27, 2022 at 08:37:31AM +0200, Juergen Gross wrote:
> > > > On 26.04.22 19:35, Borislav Petkov wrote:
> > > > > On Tue, Apr 26, 2022 at 03:40:21PM +0200, Juergen Gross wrote:
> > > > > >    /* protected virtualization */
> > > > > >    static void pv_init(void)
> > > > > >    {
> > > > > >        if (!is_prot_virt_guest())
> > > > > >            return;
> > > > > > +    platform_set_feature(PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS);
> > > > >
> > > > > Kinda long-ish for my taste. I'll probably call it:
> > > > >
> > > > >     platform_set()
> > > > >
> > > > > as it is implicit that it sets a feature bit.
> > > >
> > > > Okay, fine with me.
> > > >
> > > > > > diff --git a/arch/x86/mm/mem_encrypt_identity.c 
> > > > > > b/arch/x86/mm/mem_encrypt_identity.c
> > > > > > index b43bc24d2bb6..6043ba6cd17d 100644
> > > > > > --- a/arch/x86/mm/mem_encrypt_identity.c
> > > > > > +++ b/arch/x86/mm/mem_encrypt_identity.c
> > > > > > @@ -40,6 +40,7 @@
> > > > > >    #include <linux/mm.h>
> > > > > >    #include <linux/mem_encrypt.h>
> > > > > >    #include <linux/cc_platform.h>
> > > > > > +#include <linux/platform-feature.h>
> > > > > >    #include <asm/setup.h>
> > > > > >    #include <asm/sections.h>
> > > > > > @@ -566,6 +567,10 @@ void __init sme_enable(struct boot_params *bp)
> > > > > >        } else {
> > > > > >            /* SEV state cannot be controlled by a command line option */
> > > > > >            sme_me_mask = me_mask;
> > > > > > +
> > > > > > +        /* Set restricted memory access for virtio. */
> > > > > > +        platform_set_feature(PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS);
>
> This is way early in the boot, but it appears that marking the platform feature 
> bitmap as __read_mostly puts this in the .data section, so avoids the issue of 
> bss being cleared.

In V2 (not yet posted) I have moved the call to sev_setup_arch().

> TDX support also uses the arch_has_restricted_virtio_memory_access() function 
> and will need to be updated.

Yes.

> Seems like a lot of changes, I just wonder if the the arch_has...() function 
> couldn't be updated to also include a Xen check?

This was not seen to be a nice solution.

And TBH, I think this series is making the code much cleaner. Look at the
diffstat of this patch.


Juergen

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