On 7/9/25 03:08, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@kernel.org>
>
> The early page state change API performs an SVSM call to PVALIDATE each
> page when running under a SVSM, and this involves either a GHCB page
> based call or a call based on the MSR protocol.
>
> The GHCB page based variant involves VA to PA translation of the GHCB
> address, and this is best avoided in the startup code, where virtual
> addresses are ambiguous (1:1 or kernel virtual).
>
> As this is the last remaining occurrence of svsm_perform_call_protocol()
> in the startup code, switch to the MSR protocol exclusively in this
> particular case, so that the GHCB based plumbing can be moved out of the
> startup code entirely in a subsequent patch.
>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
With some comments below.
> ---
> arch/x86/boot/compressed/sev.c | 20 --------------------
> arch/x86/boot/startup/sev-shared.c | 4 +++-
> 2 files changed, 3 insertions(+), 21 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
> index fd1b67dfea22..b71c1ab6a282 100644
> --- a/arch/x86/boot/compressed/sev.c
> +++ b/arch/x86/boot/compressed/sev.c
> @@ -50,31 +50,11 @@ u64 svsm_get_caa_pa(void)
> return boot_svsm_caa_pa;
> }
>
> -int svsm_perform_call_protocol(struct svsm_call *call);
> -
> u8 snp_vmpl;
>
> /* Include code for early handlers */
> #include "../../boot/startup/sev-shared.c"
>
> -int svsm_perform_call_protocol(struct svsm_call *call)
> -{
> - struct ghcb *ghcb;
> - int ret;
> -
> - if (boot_ghcb)
> - ghcb = boot_ghcb;
> - else
> - ghcb = NULL;
> -
> - do {
> - ret = ghcb ? svsm_perform_ghcb_protocol(ghcb, call)
> - : svsm_perform_msr_protocol(call);
> - } while (ret == -EAGAIN);
> -
> - return ret;
> -}
> -
> static bool sev_snp_enabled(void)
> {
> return sev_status & MSR_AMD64_SEV_SNP_ENABLED;
> diff --git a/arch/x86/boot/startup/sev-shared.c b/arch/x86/boot/startup/sev-shared.c
> index 992abfa50508..1bb4b522dfaa 100644
> --- a/arch/x86/boot/startup/sev-shared.c
> +++ b/arch/x86/boot/startup/sev-shared.c
> @@ -753,7 +753,9 @@ static void __head svsm_pval_4k_page(unsigned long paddr, bool validate)
> call.rax = SVSM_CORE_CALL(SVSM_CORE_PVALIDATE);
> call.rcx = pc_pa;
>
> - ret = svsm_perform_call_protocol(&call);
> + do {
> + ret = svsm_perform_msr_protocol(&call);
> + } while (ret == -EAGAIN);
There's no comment here, like in the previous change, about why we are
using this method directly. Can one be added?
Also, this makes the second place where this do-while call to the MSR
protocol is used, maybe a common function would be good to have now.
Thanks,
Tom
> if (ret)
> sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_PVALIDATE);
>