[PATCH v7 07/22] x86/sev: Share implementation of MSR-based page state change

Ard Biesheuvel
2025-08-28T10:22:44Z

From: Ard Biesheuvel <ardb@kernel.org>

Both the decompressor and the SEV startup code implement the exact same
sequence for invoking the MSR based communication protocol to effectuate
a page state change.

Before tweaking the internal APIs used in both versions, merge them and
share them so those tweaks are only needed in a single place.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/boot/compressed/sev.c | 40 ++------------------
arch/x86/boot/startup/sev-shared.c | 35 +++++++++++++++++
arch/x86/boot/startup/sev-startup.c | 29 +-------------
3 files changed, 39 insertions(+), 65 deletions(-)

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 6c0f91d38595..f714235d3222 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -60,46 +60,12 @@ static bool sev_snp_enabled(void)
return sev_status & MSR_AMD64_SEV_SNP_ENABLED;
}

-static void __page_state_change(unsigned long paddr, enum psc_op op)
-{
- u64 val, msr;
-
- /*
- * If private -> shared then invalidate the page before requesting the
- * state change in the RMP table.
- */
- if (op == SNP_PAGE_STATE_SHARED)
- pvalidate_4k_page(paddr, paddr, false);
-
- /* Save the current GHCB MSR value */
- msr = sev_es_rd_ghcb_msr();
-
- /* Issue VMGEXIT to change the page state in RMP table. */
- sev_es_wr_ghcb_msr(GHCB_MSR_PSC_REQ_GFN(paddr >> PAGE_SHIFT, op));
- VMGEXIT();
-
- /* Read the response of the VMGEXIT. */
- val = sev_es_rd_ghcb_msr();
- if ((GHCB_RESP_CODE(val) != GHCB_MSR_PSC_RESP) || GHCB_MSR_PSC_RESP_VAL(val))
- sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_PSC);
-
- /* Restore the GHCB MSR value */
- sev_es_wr_ghcb_msr(msr);
-
- /*
- * Now that page state is changed in the RMP table, validate it so that it is
- * consistent with the RMP entry.
- */
- if (op == SNP_PAGE_STATE_PRIVATE)
- pvalidate_4k_page(paddr, paddr, true);
-}
-
void snp_set_page_private(unsigned long paddr)
{
if (!sev_snp_enabled())
return;

- __page_state_change(paddr, SNP_PAGE_STATE_PRIVATE);
+ __page_state_change(paddr, paddr, SNP_PAGE_STATE_PRIVATE);
}

void snp_set_page_shared(unsigned long paddr)
@@ -107,7 +73,7 @@ void snp_set_page_shared(unsigned long paddr)
if (!sev_snp_enabled())
return;

- __page_state_change(paddr, SNP_PAGE_STATE_SHARED);
+ __page_state_change(paddr, paddr, SNP_PAGE_STATE_SHARED);
}

bool early_setup_ghcb(void)
@@ -133,7 +99,7 @@ bool early_setup_ghcb(void)
void snp_accept_memory(phys_addr_t start, phys_addr_t end)
{
for (phys_addr_t pa = start; pa < end; pa += PAGE_SIZE)
- __page_state_change(pa, SNP_PAGE_STATE_PRIVATE);
+ __page_state_change(pa, pa, SNP_PAGE_STATE_PRIVATE);
}

void sev_es_shutdown_ghcb(void)
diff --git a/arch/x86/boot/startup/sev-shared.c b/arch/x86/boot/startup/sev-shared.c
index 68044c11524c..4c94d88f5ac8 100644
--- a/arch/x86/boot/startup/sev-shared.c
+++ b/arch/x86/boot/startup/sev-shared.c
@@ -662,6 +662,41 @@ static void __head pvalidate_4k_page(unsigned long vaddr, unsigned long paddr,
sev_evict_cache((void *)vaddr, 1);
}

+static void __head __page_state_change(unsigned long vaddr, unsigned long paddr,
+ enum psc_op op)
+{
+ u64 val, msr;
+
+ /*
+ * If private -> shared then invalidate the page before requesting the
+ * state change in the RMP table.
+ */
+ if (op == SNP_PAGE_STATE_SHARED)
+ pvalidate_4k_page(vaddr, paddr, false);
+
+ /* Save the current GHCB MSR value */
+ msr = sev_es_rd_ghcb_msr();
+
+ /* Issue VMGEXIT to change the page state in RMP table. */
+ sev_es_wr_ghcb_msr(GHCB_MSR_PSC_REQ_GFN(paddr >> PAGE_SHIFT, op));
+ VMGEXIT();
+
+ /* Read the response of the VMGEXIT. */
+ val = sev_es_rd_ghcb_msr();
+ if ((GHCB_RESP_CODE(val) != GHCB_MSR_PSC_RESP) || GHCB_MSR_PSC_RESP_VAL(val))
+ sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_PSC);
+
+ /* Restore the GHCB MSR value */
+ sev_es_wr_ghcb_msr(msr);
+
+ /*
+ * Now that page state is changed in the RMP table, validate it so that it is
+ * consistent with the RMP entry.
+ */
+ if (op == SNP_PAGE_STATE_PRIVATE)
+ pvalidate_4k_page(vaddr, paddr, true);
+}
+
/*
* Maintain the GPA of the SVSM Calling Area (CA) in order to utilize the SVSM
* services needed when not running in VMPL0.
diff --git a/arch/x86/boot/startup/sev-startup.c b/arch/x86/boot/startup/sev-startup.c
index 8a06f6026101..5eb7d939ebd3 100644
--- a/arch/x86/boot/startup/sev-startup.c
+++ b/arch/x86/boot/startup/sev-startup.c
@@ -135,7 +135,6 @@ early_set_pages_state(unsigned long vaddr, unsigned long paddr,
unsigned long npages, enum psc_op op)
{
unsigned long paddr_end;
- u64 val;

vaddr = vaddr & PAGE_MASK;

@@ -143,37 +142,11 @@ early_set_pages_state(unsigned long vaddr, unsigned long paddr,
paddr_end = paddr + (npages << PAGE_SHIFT);

while (paddr < paddr_end) {
- /* Page validation must be rescinded before changing to shared */
- if (op == SNP_PAGE_STATE_SHARED)
- pvalidate_4k_page(vaddr, paddr, false);
-
- /*
- * Use the MSR protocol because this function can be called before
- * the GHCB is established.
- */
- sev_es_wr_ghcb_msr(GHCB_MSR_PSC_REQ_GFN(paddr >> PAGE_SHIFT, op));
- VMGEXIT();
-
- val = sev_es_rd_ghcb_msr();
-
- if (GHCB_RESP_CODE(val) != GHCB_MSR_PSC_RESP)
- goto e_term;
-
- if (GHCB_MSR_PSC_RESP_VAL(val))
- goto e_term;
-
- /* Page validation must be performed after changing to private */
- if (op == SNP_PAGE_STATE_PRIVATE)
- pvalidate_4k_page(vaddr, paddr, true);
+ __page_state_change(vaddr, paddr, op);

vaddr += PAGE_SIZE;
paddr += PAGE_SIZE;
}
-
- return;
-
-e_term:
- sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_PSC);
}

void __head early_snp_set_memory_private(unsigned long vaddr, unsigned long paddr,
--
2.51.0.268.g9569e192d0-goog