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Message-ID: <BYAPR21MB16882B5A167C985B516B6E5FD79B9@BYAPR21MB1688.namprd21.prod.outlook.com>
Date: Wed, 12 Apr 2023 14:32:18 +0000
From: "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To: Tianyu Lan <ltykernel@...il.com>,
"luto@...nel.org" <luto@...nel.org>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"mingo@...hat.com" <mingo@...hat.com>,
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"x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
"seanjc@...gle.com" <seanjc@...gle.com>,
"pbonzini@...hat.com" <pbonzini@...hat.com>,
"jgross@...e.com" <jgross@...e.com>,
Tianyu Lan <Tianyu.Lan@...rosoft.com>,
"kirill@...temov.name" <kirill@...temov.name>,
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"pawan.kumar.gupta@...ux.intel.com"
<pawan.kumar.gupta@...ux.intel.com>,
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CC: "pangupta@....com" <pangupta@....com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: RE: [RFC PATCH V4 06/17] x86/hyperv: decrypt VMBus pages for sev-snp
enlightened guest
From: Tianyu Lan <ltykernel@...il.com> Sent: Monday, April 3, 2023 10:44 AM
>
The Subject prefix for this patch is still wrong. I previously commented on
this. :-( It should be Drivers: hv: vmbus:
> VMBus post msg, synic event and message pages are shared
> with hypervisor and so decrypt these pages in the sev-snp guest.
>
> Signed-off-by: Tianyu Lan <tiala@...rosoft.com>
> ---
> Change since RFC V3:
> * Set encrypt page back in the hv_synic_free()
>
> Change since RFC V2:
> * Fix error in the error code path and encrypt
> pages correctly when decryption failure happens.
> ---
> drivers/hv/hv.c | 42 +++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 41 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
> index 008234894d28..e09cea8f2f04 100644
> --- a/drivers/hv/hv.c
> +++ b/drivers/hv/hv.c
> @@ -20,6 +20,7 @@
> #include <linux/interrupt.h>
> #include <clocksource/hyperv_timer.h>
> #include <asm/mshyperv.h>
> +#include <linux/set_memory.h>
> #include "hyperv_vmbus.h"
>
> /* The one and only */
> @@ -117,7 +118,7 @@ int hv_post_message(union hv_connection_id connection_id,
>
> int hv_synic_alloc(void)
> {
> - int cpu;
> + int cpu, ret;
> struct hv_per_cpu_context *hv_cpu;
>
> /*
> @@ -168,9 +169,39 @@ int hv_synic_alloc(void)
> pr_err("Unable to allocate post msg page\n");
> goto err;
> }
> +
> + if (hv_isolation_type_en_snp()) {
> + ret = set_memory_decrypted((unsigned long)
> + hv_cpu->synic_message_page, 1);
> + if (ret)
> + goto err;
> +
> + ret = set_memory_decrypted((unsigned long)
> + hv_cpu->synic_event_page, 1);
> + if (ret)
> + goto err_decrypt_event_page;
> +
> + ret = set_memory_decrypted((unsigned long)
> + hv_cpu->post_msg_page, 1);
> + if (ret)
> + goto err_decrypt_msg_page;
> +
> + memset(hv_cpu->synic_message_page, 0, PAGE_SIZE);
> + memset(hv_cpu->synic_event_page, 0, PAGE_SIZE);
> + memset(hv_cpu->post_msg_page, 0, PAGE_SIZE);
> + }
> }
>
> return 0;
> +
> +err_decrypt_msg_page:
> + set_memory_encrypted((unsigned long)
> + hv_cpu->synic_event_page, 1);
> +
> +err_decrypt_event_page:
> + set_memory_encrypted((unsigned long)
> + hv_cpu->synic_message_page, 1);
> +
> err:
> /*
> * Any memory allocations that succeeded will be freed when
> @@ -191,6 +222,15 @@ void hv_synic_free(void)
> free_page((unsigned long)hv_cpu->synic_event_page);
> free_page((unsigned long)hv_cpu->synic_message_page);
> free_page((unsigned long)hv_cpu->post_msg_page);
> +
> + if (hv_isolation_type_en_snp()) {
> + set_memory_encrypted((unsigned long)
> + hv_cpu->synic_message_page, 1);
> + set_memory_encrypted((unsigned long)
> + hv_cpu->synic_event_page, 1);
> + set_memory_encrypted((unsigned long)
> + hv_cpu->post_msg_page, 1);
> + }
The re-encryption must be done *before* pages are freed!
Furthermore, if the re-encryption fails, we should not free
the page as it would pollute the free memory pool. The best
we can do is leak the memory. See Patch 5 in Dexuan's
TDX series, which does the same thing (but still doesn't
get it quite right, per my comments).
Michael
> }
>
> kfree(hv_context.hv_numa_map);
> --
> 2.25.1
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