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

From: Juergen Gross
Date: Wed Apr 27 2022 - 10:14:23 EST

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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